Remove markdown.tmbundle from `markdown language features` extension

The grammar is contributed by the language basics extension

extensions/markdown-language-features/cgmanifest.json

-{
-	"registrations": [
-		{
-			"component": {
-				"type": "git",
-				"git": {
-					"name": "textmate/markdown.tmbundle",
-					"repositoryUrl": "https://github.com/textmate/markdown.tmbundle",
-					"commitHash": "11cf764606cb2cde54badb5d0e5a0758a8871c4b"
-				}
-			},
-			"licenseDetail": [
-				"Copyright (c) markdown.tmbundle authors",
-				"",
-				"If not otherwise specified (see below), files in this repository fall under the following license:",
-				"",
-				"Permission to copy, use, modify, sell and distribute this",
-				"software is granted. This software is provided \"as is\" without",
-				"express or implied warranty, and with no claim as to its",
-				"suitability for any purpose.",
-				"",
-				"An exception is made for files in readable text which contain their own license information,",
-				"or files where an accompanying file exists (in the same directory) with a \"-license\" suffix added",
-				"to the base-name name of the original file, and an extension of txt, html, or similar. For example",
-				"\"tidy\" is accompanied by \"tidy-license.txt\"."
-			],
-			"license": "TextMate Bundle License",
-			"version": "0.0.0"
-		}
-	],
-	"version": 1
-}
\ No newline at end of file