stand/lua: Remove inaccurate comment after r329590

lualoader does a pretty good job of reverting any environment changes now.
It will even wipe out boot_verbose if it's set explicitly in loader.conf(5)
and overwritten in the boot options menu.

Future work will likely change this, as explicit choices made in the menu
should probably override the new loader.conf(5). I don't suspect this will
cause much grief, though, so it is not a high priority until boot
environment support actually lands.