Changes

Only render/remove submenus when menu is rendered or rendering

Added the 'or rendering' part. Otherwise rendering of the submenus will
fail when called through a render method (of the menu itself) method
instead of a menu action.

Menu: remove unnecessary fix for a problem that was caused by not
rendering the submenus correctly.

Change-Id: I98e12c0d286478eab774672873f8fa4b1e98d627
Signed-off-by: Ralf Muri <ralf.muri@bsi-software.com>
Reviewed-on: https://git.eclipse.org/r/160191
Tested-by: CI Bot
Reviewed-by: Roger Stebler <roger.stebler@bsi-software.com>