display: Clean up whitespace
display: Remove extraneous checks for grab_window

We assert a few lines down anyway, so just move the asserts up
and kill the if statement.
display: Fix tiling when grabbing an attached dialog

It seems we used the wrong variable by accident
display: Make sure to retrieve the toplevel transient for

If we have multiple modal stacked dialogs, move the top one, not
the immediate parent, which heavily confuses mutter.
display: Remove the same checks in end_grab_op
keybindings: Remove now-unused meta_screen_grab_all_keys
window: Move X11 struts implementation to X11 codepath