Revert "xfs: use iomap_valid method to detect stale cached iomaps"

This reverts commit ea67e731 which is
commit 304a68b9 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I371fe53ba28e2f032a4befb0f3e8d006d52a7167
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>