project: Drop --no-deref from update-ref --stdin

repo calls `git update-ref --stdin` when updating multiple refs during
repo init and repo sync. Historically, `--no-deref` was also passed.

Older Git 2.17 which we still support rejects the combination of
`--stdin` and `--no-deref`, emitting a usage error even when the stdin
input is valid.

The `--no-deref` option is only meaningful when updating symbolic refs
such as HEAD. The stdin-based update-ref path only operates on explicit
refs (tags, remote refs, alternates) and never symbolic refs.

Remove the unnecessary option to restore compatibility with Git 2.17
while preserving identical behavior on newer Git versions.

Tested with:
  - Git 2.17.1
  - Git 2.34.1

Change-Id: I22001de03800f5699b26a40bc1fb1fec002ed048
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/571721
Reviewed-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Enei <miyako.enei@alpsalpine.com>
Tested-by: Enei <miyako.enei@alpsalpine.com>

project.py

@@ -2673,7 +2673,7 @@ class Project:
                 if update_ref_cmds:
                     GitCommand(
                         self,
-                        ["update-ref", "--no-deref", "--stdin"],
+                        ["update-ref", "--stdin"],
                         bare=True,
                         input="".join(update_ref_cmds),
                     ).Wait()
@@ -2921,7 +2921,7 @@ class Project:
                     )
                     GitCommand(
                         self,
-                        ["update-ref", "--no-deref", "--stdin"],
+                        ["update-ref", "--stdin"],
                         bare=True,
                         input=delete_cmds,
                         log_as_error=False,