QUIC: do not send STOP_SENDING after STREAM fin.

QUIC: do not send STOP_SENDING after STREAM fin.

Previously STOP_SENDING was sent to client upon stream closure if rev->eof and
rev->error were not set.  This was an indirect indication that no RESET_STREAM
or STREAM fin has arrived.  But it is indeed possible that rev->eof is not set,
but STREAM fin has already been received, just not read out by the application.
In this case sending STOP_SENDING does not make sense and can be misleading for
some clients.