Remove VSIX publishing support

eng/config/PublishVsix.MyGet.config

-<?xml version="1.0" encoding="utf-8"?>
-<!--
-  The list of VSIX extensions we produce and upload to myget.org. Currently the script (PostTest.ps1) that
-  we run after every signed build uploads all shipped extensions in the VSIX folder to myget.org
- -->
-<extensions>
-  <extension id="Microsoft.VisualStudio.IntegrationTest.Setup"/>
-  <extension id="Roslyn.VisualStudio.DiagnosticsWindow"/>
-  <extension id="Roslyn.Compilers.Extension"/>
-  <extension id="ExpressionEvaluatorPackage"/>
-  <extension id="Roslyn.VisualStudio.Setup"/>
-</extensions>

eng/publish-assets.ps1

 # Publishes our build assets to nuget, myget, dotnet/versions, etc ..
 #
-# The publish operation is best visioned as an optional yet repeatable post build operation. It can be 
-# run anytime after build or automatically as a post build step. But it is an operation that focuses on 
+# The publish operation is best visioned as an optional yet repeatable post build operation. It can be
+# run anytime after build or automatically as a post build step. But it is an operation that focuses on
 # build outputs and hence can't rely on source code from the build being available
 #
-# Repeatable is important here because we have to assume that publishes can and will fail with some 
-# degree of regularity. 
+# Repeatable is important here because we have to assume that publishes can and will fail with some
+# degree of regularity.
 [CmdletBinding(PositionalBinding=$false)]
 Param(
   # Standard options
@@ -14,7 +14,7 @@ Param(
   [string]$releaseName = "",
   [switch]$test,
 
-  # Credentials 
+  # Credentials
   [string]$gitHubUserName = "",
   [string]$gitHubToken = "",
   [string]$gitHubEmail = "",
@@ -52,7 +52,7 @@ function Publish-Nuget($publishData, [string]$packageDir) {
       if (-not (Test-Path $nupkg)) {
         throw "$nupkg does not exist"
       }
-      
+
       # Lookup the feed name from the packages map using the package name without the version or extension.
       $nupkgWithoutVersion = $nupkg -replace '(\.\d){3}-.*.nupkg', ''
       if (-not (Get-Member -InputObject $packagesData -Name $nupkgWithoutVersion)) {
@@ -66,12 +66,12 @@ function Publish-Nuget($publishData, [string]$packageDir) {
         Write-Host "    Skipping publishing for $nupkg as it is published by arcade"
         continue
       }
-      
+
       # Use the feed name to get the source to upload the package to.
       if (-not (Get-Member -InputObject $feedData -Name $feedName)) {
         throw "$feedName has no configured source feed"
       }
-      
+
       $uploadUrl = $feedData.$feedName
       $apiKey = Get-PublishKey $uploadUrl
 
@@ -85,38 +85,18 @@ function Publish-Nuget($publishData, [string]$packageDir) {
   }
 }
 
-function Publish-Vsix([string]$uploadUrl) {
-  Write-Host "Publishing VSIX to $uploadUrl"
-  $apiKey = Get-PublishKey $uploadUrl
-  $extensions = [xml](Get-Content (Join-Path $EngRoot "config\PublishVsix.MyGet.config"))
-  foreach ($extension in $extensions.extensions.extension) {
-    $vsix = Join-Path $VSSetupDir ($extension.id + ".vsix")
-    if (-not (Test-Path $vsix)) {
-      throw "VSIX $vsix does not exist"
-    }
-    
-    Write-Host "  Publishing '$vsix'"
-    if (-not $test) { 
-      $response = Invoke-WebRequest -Uri $uploadUrl -Headers @{"X-NuGet-ApiKey"=$apiKey} -ContentType 'multipart/form-data' -InFile $vsix -Method Post -UseBasicParsing
-      if ($response.StatusCode -ne 201) {
-        throw "Failed to upload VSIX extension: $vsix. Upload failed with Status code: $response.StatusCode"
-      }
-    }
-  }
-}
-
 function Publish-Channel([string]$packageDir, [string]$name) {
   $publish = GetProjectOutputBinary "RoslynPublish.exe"
   $args = "-nugetDir `"$packageDir`" -channel $name -gu $gitHubUserName -gt $gitHubToken -ge $githubEmail"
   Write-Host "Publishing $packageDir to channel $name"
-  if (-not $test) { 
+  if (-not $test) {
     Exec-Console $publish $args
   }
 }
 
 # Do basic verification on the values provided in the publish configuration
-function Test-Entry($publishData, [switch]$isBranch) { 
-  if ($isBranch) { 
+function Test-Entry($publishData, [switch]$isBranch) {
+  if ($isBranch) {
     foreach ($nugetKind in $publishData.nugetKind) {
       if ($nugetKind -ne "PerBuildPreRelease" -and $nugetKind -ne "Shipping" -and $nugetKind -ne "NonShipping") {
                     throw "Branches are only allowed to publish Shipping, NonShipping, or PerBuildPreRelease"
@@ -125,8 +105,8 @@ function Test-Entry($publishData, [switch]$isBranch) {
   }
 }
 
-# Publish a given entry: branch or release. 
-function Publish-Entry($publishData, [switch]$isBranch) { 
+# Publish a given entry: branch or release.
+function Publish-Entry($publishData, [switch]$isBranch) {
   Test-Entry $publishData -isBranch:$isBranch
 
   # First publish the NuGet packages to the specified feeds
@@ -134,12 +114,6 @@ function Publish-Entry($publishData, [switch]$isBranch) {
     Publish-NuGet $publishData (Join-Path $PackagesDir $nugetKind)
   }
 
-  # Next publish the VSIX to the specified feeds
-  $vsixData = $publishData.vsix
-  if ($vsixData -ne $null) { 
-    Publish-Vsix $vsixData
-  }
-
   # Finally get our channels uploaded to versions
   foreach ($channel in $publishData.channels) {
     foreach ($nugetKind in $publishData.nugetKind) {