serial-parsers,port-serial-at: move echo removal into serial parser

Mainly because we need somewhere to stash the call end regex, and
it's silly to have a 3rd instance of that in MMPortSerialAt when
we already have one in the serial parsers that MMPortSerialAt
relies on pretty heavily.

Signed-off-by: Dan Williams <dan@ioncontrol.co>

src/plugins/wavecom/mm-broadband-modem-wavecom.c

@@ -1245,6 +1245,7 @@ setup_ports (MMBroadbandModem *self)
 
     mm_port_serial_at_set_response_parser (MM_PORT_SERIAL_AT (primary),
                                            mm_serial_parser_v1_parse,
+                                           mm_serial_parser_v1_remove_echo,
                                            parser,
                                            mm_serial_parser_v1_destroy);
 }