mptcp: revert "mptcp: provide subflow aware release function"

[ Upstream commit 0a3cc579 ]

This change reverts commit ad98dd37 ("mptcp: provide subflow aware
release function"). The latter introduced a deadlock spotted by
syzkaller and is not needed anymore after the previous commit.

Fixes: ad98dd37

 ("mptcp: provide subflow aware release function")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>