tcp: no longer release socket ownership in tcp_release_cb()

This partially reverts c3f9b018 ("tcp: tcp_release_cb()
should release socket ownership").

prequeue has been removed by Florian in commit e7942d06
("tcp: remove prequeue support")

__tcp_checksum_complete_user() being gone, we no longer
have to release socket ownership in tcp_release_cb().

This is a prereq for third patch in the series
("net: call prot->release_cb() when processing backlog").

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>