refactor!: remove go-git backend (#39487)

Removes the go-git backend so every build uses the git CLI backend. Its
Windows performance advantage is gone, it lacks SHA-256 support, and it
breaks repositories on Windows.

The performance changes moved to
https://github.com/go-gitea/gitea/pull/39526.

Fixes https://github.com/go-gitea/gitea/issues/38359
Fixes https://github.com/go-gitea/gitea/issues/34694

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/parse_treeentry.go

@@ -43,8 +43,6 @@ func parseTreeEntries(data []byte, ptree *Tree) ([]*TreeEntry, error) {
 	return entries, nil
 }
 
-var _ = catBatchParseTreeEntries // bypass "unused" lint because it is only used by "nogogit"
-
 func catBatchParseTreeEntries(objectFormat ObjectFormat, ptree *Tree, rd BufferedReader, sz int64) ([]*TreeEntry, error) {
 	entries := make([]*TreeEntry, 0, 10)