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/bts_osmo.py b/src/osmo_gsm_tester/bts_osmo.py
index 60b9695..be87b9d 100644
--- a/src/osmo_gsm_tester/bts_osmo.py
+++ b/src/osmo_gsm_tester/bts_osmo.py
@@ -21,7 +21,7 @@
 import pprint
 import tempfile
 from abc import ABCMeta, abstractmethod
-from . import log, config, util, template, process, event_loop, bts, pcu_osmo
+from . import log, config, util, template, process, bts, pcu_osmo
 
 class OsmoBts(bts.Bts, metaclass=ABCMeta):
     proc_bts = None