af_unix: Don't check SOCK_DEAD in unix_stream_read_skb().

af_unix: Don't check SOCK_DEAD in unix_stream_read_skb().

unix_stream_read_skb() checks SOCK_DEAD only when the dequeued skb is
OOB skb.

unix_stream_read_skb() is called for a SOCK_STREAM socket in SOCKMAP
when data is sent to it.

The function is invoked via sk_psock_verdict_data_ready(), which is
set to sk->sk_data_ready().

During sendmsg(), we check if the receiver has SOCK_DEAD, so there
is no point in checking it again later in ->read_skb().

Also, unix_read_skb() for SOCK_DGRAM does not have the test either.

Let's remove the SOCK_DEAD test in unix_stream_read_skb().

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250702223606.1054680-3-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>