e2e: Implicitely include the handshake in all tests

Instead of having to write it manually everytime

tests/end_to_end/scenarios/irc_server_presence_subscription.py

@@ -1,7 +1,6 @@
 from scenarios import *
 
 scenario = (
-    sequences.handshake(),
     send_stanza("<presence type='subscribe' from='{jid_one}/{resource_one}' to='{irc_server_one}' id='sub1' />"),
     expect_stanza("/presence[@to='{jid_one}'][@from='{irc_server_one}'][@type='subscribed']"),
 )