sctp: remove the unnecessary sinfo_stream check in sctp_prsctp_prune_unsent

[ Upstream commit 9f0b7732 ]

Since commit 5bbbbe32 ("sctp: introduce stream scheduler foundations"),
sctp_stream_outq_migrate() has been called in sctp_stream_init/update to
removes those chunks to streams higher than the new max. There is no longer
need to do such check in sctp_prsctp_prune_unsent().

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 2f201ae1 ("sctp: clear out_curr if all frag chunks of current msg are pruned")
Signed-off-by: Sasha Levin <sashal@kernel.org>