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>

custom/conf/app.example.ini

@@ -780,8 +780,6 @@ LEVEL = Info
 ;; Respond to pushes to a non-default branch with a URL for creating a Pull Request (if the repository has them enabled)
 ;PULL_REQUEST_PUSH_MESSAGE = true
 ;;
-;; (Go-Git only) Don't cache objects greater than this in memory. (Set to 0 to disable.)
-;LARGE_OBJECT_THRESHOLD = 1048576
 ;; Set to true to forcibly set core.protectNTFS=false
 ;DISABLE_CORE_PROTECT_NTFS=false
 ;; Disable the usage of using partial clones for git.