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

This reverts commit aed0aac1 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: Ib364e34f99f0350e81819022fb2eb1fd060b3ddd
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>