src.ctf.lttng-live: live_..._list_sessions(): remove handshake

src.ctf.lttng-live: live_..._list_sessions(): remove handshake

The only user of live_viewer_connection_list_sessions() is
lttng_live_query_list_sessions() which calls
live_viewer_connection_create() before. live_viewer_connection_create()
calls lttng_live_connect_viewer() which calls lttng_live_handshake().

There is no need to call lttng_live_handshake() twice. This makes the
relay daemon assign two viewer IDs to the CLI, as seen in Wireshark.

Babeltrace 1.5 does not send the "connect" command twice either.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I640b9397c21ca37ad5c841415b5ed0c12193825a
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1798