perf(repo): fetch the initial commit instead of pushing it (#39628)

Creating a repository with an initial commit, via `auto_init` or a
template with git content, pushed that commit through receive-pack and
three server-side hooks that do nothing for this internal push except
refresh server info. Fetching it into the bare repository instead makes
such repository creation about 3.7x faster locally (median 790ms to
214ms). E2E tests that create initialized repositories get about
0.2-0.3s faster each.

1. Run `update-server-info` after template content generation, which the
push's `post-receive` hook did before.
2. Remove the now unused `InternalPushingEnvironment` and
`PushOptions.LocalRefName`.

modules/git/repo.go

@@ -226,7 +226,6 @@ func Clone(ctx context.Context, from, to string, opts CloneRepoOptions) error {
 // PushOptions options when push to remote
 type PushOptions struct {
 	Remote         string
-	LocalRefName   string
 	Branch         string
 	Force          bool
 	ForceWithLease string
@@ -248,13 +247,7 @@ func Push(ctx context.Context, localRepoPath string, opts PushOptions) error {
 	}
 	remoteBranchArgs := []string{opts.Remote}
 	if len(opts.Branch) > 0 {
-		var refspec string
-		if opts.LocalRefName != "" {
-			refspec = fmt.Sprintf("%s:%s", opts.LocalRefName, opts.Branch)
-		} else {
-			refspec = opts.Branch
-		}
-		remoteBranchArgs = append(remoteBranchArgs, refspec)
+		remoteBranchArgs = append(remoteBranchArgs, opts.Branch)
 	}
 	cmd.AddDashesAndList(remoteBranchArgs...)