MINOR: quic: do not remove qc_stream_desc automatically on ACK handling

MINOR: quic: do not remove qc_stream_desc automatically on ACK handling

qc_stream_desc_ack() is used to handle ACK received for STREAM frame. It
removes acknowledged data from their underlying buffer.

If all data were removed after ACK handling, qc_stream_desc instance
would automatically be freed at the end of qc_stream_desc_ack().
However, this renders the function complicated to use. Simplify this by
removing this automatic removal. Now, caller is responsible to check
after ACK handling if qc_stream_desc instance can be removed. This is
easily done using qc_stream_desc_done() helper.