function callPendingCbs(c) {
      const el = c.el;
      if (el._moveCb) {
          el._moveCb();
      }
      if (el._enterCb) {
          el._enterCb();
      }
  }
TransitionGroup does not support "mode" so we need to remove it from the
props declarations, but direct delete operation is considered a side effect
and will make the entire transition feature non-tree-shakeable, so we do it
in a function and mark the function's invocation as pure.