Drop event_loop global functions and import MainLoop

Take the chance to identify and drop modules importing event_loop but
not using it.

Change-Id: Ifa1940cd00138ebc72fbcfd45a0e28246f7a5ed9
diff --git a/src/osmo_gsm_tester/pcu_osmo.py b/src/osmo_gsm_tester/pcu_osmo.py
index deaeb80..6ab97de 100644
--- a/src/osmo_gsm_tester/pcu_osmo.py
+++ b/src/osmo_gsm_tester/pcu_osmo.py
@@ -20,7 +20,7 @@
 import os
 import pprint
 import tempfile
-from . import log, config, util, template, process, event_loop, pcu
+from . import log, config, util, template, process, pcu
 
 class OsmoPcu(pcu.Pcu):
     inst = None