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

This reverts commit 1b6de5e6 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: Ifbb679aeb516ec0b393a1996c0e3f51db2ae2ab5
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>