Revert the change to do_cmdline_cmd() from #5226.
This function is used in many places, so making it different from Vim
leads to small differences from Vim in the behavior of some functions
like execute() and assert_fails(). If DOCMD_VERBOSE really needs to be
removed somewhere, a do_cmdline() call without DOCMD_VERBOSE is also
shorter than a do_cmdline() call with DOCMD_VERBOSE.