Revert "drm/ast: Use drm_aperture_remove_conflicting_pci_framebuffers"

This reverts commit cd1f889c which is
commit c1ebead3 upstream.

It breaks the Android ABI and can be brought back later in an abi-safe
way if needed.

Bug: 161946584
Change-Id: Id6345a15790f5e3209485004ebe071119684859b
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>