cleanup: Use g_clear_handle_id() for g_source_remove()

It makes sure we do not forget to zero the id and lets us avoid
zero checks before. We use it for all new code, lets clean up the
existing code base.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/845

src/shell-perf-log.c

@@ -218,8 +218,7 @@ shell_perf_log_set_enabled (ShellPerfLog *perf_log,
         }
       else
         {
-          g_source_remove (perf_log->statistics_timeout_id);
-          perf_log->statistics_timeout_id = 0;
+          g_clear_handle_id (&perf_log->statistics_timeout_id, g_source_remove);
         }
     }
 }