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

This reverts commit 9705f447 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: I049667ee9c932c352643b7f1c743b2025c4b284c
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>