serve: inline checkrepo() that is used only when --stdio is specified

Since e811b93f2cb1, --cmdserver is allowed to start without repository, so
checkrepo() function is meaningless.

mercurial/commands.py

@@ -5245,13 +5245,10 b' def serve(ui, repo, **opts):'
     if opts["stdio"] and opts["cmdserver"]:
         raise util.Abort(_("cannot use --stdio with --cmdserver"))
 
-    def checkrepo():
+    if opts["stdio"]:
         if repo is None:
             raise error.RepoError(_("there is no Mercurial repository here"
                               " (.hg not found)"))
-
-    if opts["stdio"]:
-        checkrepo()
         s = sshserver.sshserver(ui, repo)
         s.serve_forever()