e2e: Implicitely include the handshake in all tests

Instead of having to write it manually everytime

tests/end_to_end/scenarios/simple_channel_join_fixed.py

@@ -3,7 +3,6 @@ from scenarios import *
 conf = "fixed_server"
 
 scenario = (
-    sequences.handshake(),
     send_stanza("<presence from='{jid_one}/{resource_one}' to='#foo@{biboumi_host}/{nick_one}' />"),
     sequences.connection("irc.localhost", '{jid_one}/{resource_one}', fixed_irc_server=True),
     expect_stanza("/message/body[text()='Mode #foo [+nt] by {irc_host_one}']"),