Revert "inet: inet_defrag: prevent sk release while still in use"

This reverts commit f4877225 which is
commit 18685451 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: I67b409647431367a105d600d7fdc7a4f98273efc
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>