First, if you want to remove a scenery, it's best to use its uninstaller.
If you want to *temporary* disable, just disable it, not remove it.
If you think that by disabling an FSDT scenery from the Library, you'll save some memory, that's an entirely wasted effort, since we do custom memory management outside FSX, so the objects of a scenery will be removed from RAM as soon as you exit the airport.