Revert "blk-iocost: do not WARN if iocg was already offlined"

This reverts commit 56a9d07f which is
commit 01bc4fda 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: Id147c362bdb93706e72be53a6aa82ac00b5d9820
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>