Remove "Diff" language.

Zed now ships support for diff/patch files as a 1st class language.
See:
- zed-industries/zed#19129

Closes zed-extensions#3

Author: notpeter

extension.toml

@@ -6,10 +6,6 @@ authors = [ "d1y <[email protected]>" ]
 description = "Provides Git Syntax Highlighting"
 repository = "https://github.com/d1y/git_firefly"
 
-[grammars.diff]
-repository = "https://github.com/the-mikedavis/tree-sitter-diff"
-commit = "c165725c28e69b36c5799ff0e458713a844f1aaf"
-
 [grammars.git_commit]
 repository = "https://github.com/the-mikedavis/tree-sitter-git-commit"
 commit = "6f193a66e9aa872760823dff020960c6cedc37b3"