Revert "iomap: write iomap validity checks"

This reverts commit 54a37e5d which is
commit d7b64041 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: I8df6cb973e6b4bc0acdb60fe95d45951354364dd
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>