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

This reverts commit 4318608d 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: I43742b5a0db4105e04b1a641c91d3d48741bcfff
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>