Drop link to TextMate

This grammar has not been updated since 2016:
https://github.com/textmate/git.tmbundle/blob/master/Syntaxes/Git%20Commit%20Message.tmLanguage

The upstream test suite requires running a Ruby version that has been
EOL since 2014, and that I failed to build on macOS:
textmate/git.tmbundle#59

If this change is accepted, my plan is to add support to vscode for
highlighting non-English commit messages:
textmate/git.tmbundle#60

And even if I never get around to that, this at least opens up the
possibility for somebody else to do that.

extensions/git/syntaxes/git-commit.tmLanguage.json

@@ -1,10 +1,4 @@
 {
-	"information_for_contributors": [
-		"This file has been converted from https://github.com/textmate/git.tmbundle/blob/master/Syntaxes/Git%20Commit%20Message.tmLanguage",
-		"If you want to provide a fix or improvement, please create a pull request against the original repository.",
-		"Once accepted there, we are happy to receive an update request."
-	],
-	"version": "https://github.com/textmate/git.tmbundle/commit/93897a78c6e52bef13dadc0d4091d203c5facb40",
 	"name": "Git Commit Message",
 	"scopeName": "text.git-commit",
 	"patterns": [
@@ -138,4 +132,4 @@
 			]
 		}
 	}
-}
+}