Clean-up after SDK 6.0 P4 bump (#54149)

* Delete scripts.csproj

* Update build.proj

src/tests/Common/scripts/scripts.csproj

-<Project Sdk="Microsoft.Build.NoTargets">
-  <PropertyGroup>
-    <TargetFramework>netstandard1.3</TargetFramework>
-    <RuntimeIdentifiers>win7-x86;win7-x64</RuntimeIdentifiers>
-    <IsTestProject>false</IsTestProject>
-  </PropertyGroup>
-  <ItemGroup>
-    <!--<PackageReference Include="Microsoft.DotNet.xunit.performance.run.core" Version="1.0.0-alpha-build0040" />
-    <PackageReference Include="Microsoft.DotNet.xunit.performance.analysis.cli" Version="1.0.0-alpha-build0040" />
-    <PackageReference Include="Microsoft.DotNet.xunit.performance.runner.cli" Version="1.0.0-alpha-build0040" />
-    <PackageReference Include="Microsoft.DotNet.xunit.performance" Version="1.0.0-alpha-build0040" />
-    <PackageReference Include="Microsoft.DotNet.XUnitConsoleRunner" Version="$(MicrosoftDotNetXUnitConsoleRunnerVersion)" />
-    <PackageReference Include="Microsoft.DotNet.BuildTools.TestSuite" Version="1.0.0-prerelease-00629-04" />-->
-  </ItemGroup>
-</Project>

src/tests/build.proj

-<?xml version="1.0" encoding="utf-8"?>
-<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project DefaultTargets="Build">
   <Import Project="Directory.Build.props" />
 
   <ItemGroup>
     <Project Include="$(MSBuildThisFileDirectory)Common\dirs.proj" />
   </ItemGroup>
 
-  <Import Project="$(RepoRoot)\src\tests\Directory.Build.targets" />
-
-  <Import Project="$(RepoRoot)\src\tests\Common\dir.traversal.targets" />
+  <Import Project="Directory.Build.targets" />
+  <Import Project="Common\dir.traversal.targets" />
 
   <PropertyGroup>
     <TraversalBuildDependsOn>
@@ -18,18 +16,17 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <RestoreProjects Include="$(MSBuildThisFileDirectory)Common\scripts\scripts.csproj" />
-    <RestoreProjects Include="$(MSBuildThisFileDirectory)Common\test_dependencies_fs\test_dependencies.fsproj" />
-    <RestoreProjects Include="$(MSBuildThisFileDirectory)Common\test_dependencies\test_dependencies.csproj" />
-    <RestoreProjects Include="$(MSBuildThisFileDirectory)Common\CoreCLRTestLibrary\CoreCLRTestLibrary.csproj" />
-    <RestoreProjects Include="$(MSBuildThisFileDirectory)Common\external\external.csproj" />
-    <RestoreProjects Include="$(MSBuildThisFileDirectory)Common\ilasm\ilasm.ilproj" />
+    <RestoreProjects Include="Common\test_dependencies_fs\test_dependencies.fsproj" />
+    <RestoreProjects Include="Common\test_dependencies\test_dependencies.csproj" />
+    <RestoreProjects Include="Common\CoreCLRTestLibrary\CoreCLRTestLibrary.csproj" />
+    <RestoreProjects Include="Common\external\external.csproj" />
+    <RestoreProjects Include="Common\ilasm\ilasm.ilproj" />
   </ItemGroup>
 
   <Target Name="BuildTargetingPack" AfterTargets="BatchRestorePackages" Condition="$(__SkipTargetingPackBuild) != 'true'">
     <Message Text="Building Targeting Pack" Importance="High" />
-    <Error  Text="TargetOS has not been specified. Please do that then run build again."  Condition="'$(TargetOS)' == 'AnyOS'" />
-    <MSBuild Projects="$(MSBuildThisFileDirectory)Common\external\external.csproj"
+    <Error Text="TargetOS has not been specified. Please do that then run build again." Condition="'$(TargetOS)' == 'AnyOS'" />
+    <MSBuild Projects="Common\external\external.csproj"
              Targets="Build" />
   </Target>