Setting push_undo to FALSE in these functions is premature -- let
this stuff be handled at the actual point where the undo is
pushed, which might correspond to a different item than the one for
which gimp_item_{start,end}_move() was called.

In particular, when removing a layer from the image,
gimp_item_end_move() is called (with push_undo == TRUE) on the
layer after it's been removed, but we still need the appropriate
undo enrties to be pushed for the affected group layers.