Remove git_commit syntax highlighting from core Zed (#9025)

Fallback to extension
https://github.com/zed-industries/extensions/pull/307

Release Notes:

- Remove git_commit syntax highlighting from Zed core, `git-firefly` extension replaced that

Co-authored-by: William Desportes <williamdes@wdes.fr>
Co-authored-by: Kirill Bulatov <mail4score@gmail.com>
Co-authored-by: Marshall Bowers <1486634+maxdeviant@users.noreply.github.com>

docs/src/languages/gitcommit.md

@@ -1,4 +0,0 @@
-# Git Commit
-
-- Tree Sitter: [tree-sitter-gitcommit](https://github.com/gbprod/tree-sitter-gitcommit)
-- Language Server: N/A