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

This reverts commit 7d215e01 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: I9d1e63f0cb8187cfdafc8f75c5aa43178847c1cc
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>