Revert "Support git safe directory for manifest in subdirectory"

This reverts commit 7d6496d.

As described in
#395 we
cannot use `git rev-parse --show-toplevel` to find the root directory of
the repository in order to mark it as safe – because `git` refuses to
operate on a directory with dubious ownership, which is what we are
trying to fix!

We will need an alternative solution but for the meantime, revert this
change to fix the common case where the manifest is in the root
directory.

src/main.py

@@ -128,15 +128,6 @@ def check_call(args):
     subprocess.check_call(args)
 
 
-def get_manifest_git_checkout(manifest: t.Union[Path, str]) -> str:
-    manifest_dir = os.path.dirname(manifest)
-    output = subprocess.check_output(
-        ["git", "rev-parse", "--show-toplevel"],
-        cwd=manifest_dir,
-    )
-    return output.decode("utf-8").strip()
-
-
 def ensure_git_safe_directory(checkout: t.Union[Path, str]):
     uid = os.getuid()
     checkout_uid = os.stat(checkout).st_uid
@@ -460,7 +451,7 @@ async def run_with_args(args: argparse.Namespace) -> t.Tuple[int, int, bool]:
     if should_update and outdated_num > 0:
         changes = manifest_checker.update_manifests()
         if changes and not args.edit_only:
-            git_checkout = get_manifest_git_checkout(args.manifest)
+            git_checkout = os.path.dirname(args.manifest)
             ensure_git_safe_directory(git_checkout)
             with indir(git_checkout):
                 committed_changes = commit_changes(changes)