CLEANUP: stream-int: remove a redundant clearing of the linger_risk flag

CLEANUP: stream-int: remove a redundant clearing of the linger_risk flag

In stream_sock_read0(), we used to clear this flag. But the only case
where stream_sock_read0() is called is in reaction with a conn_sock_read0()
event coming from the lower layers, which already clears this flag. So let's
remove this duplicate one and clear one of the few remaining layering
violations in this area.