vim-patch:9.1.1667: Another outdated comment in eval.c (#35438)

Problem:  Another outdated comment in eval.c (after 9.1.1665).
Solution: Remove that comment as well. Add a few more tests for mapnew()
          that fail without patch 8.2.1672 (zeertzjq).

closes: vim/vim#18089

6b56711804

src/nvim/eval.c

@@ -2553,7 +2553,6 @@ void clear_evalarg(evalarg_T *evalarg, exarg_T *eap)
 /// Handle zero level expression.
 /// This calls eval1() and handles error message and nextcmd.
 /// Put the result in "rettv" when returning OK and "evaluate" is true.
-/// Note: "rettv.v_lock" is not set.
 ///
 /// @param evalarg  can be NULL, &EVALARG_EVALUATE or a pointer.
 ///