First round of clean-ups of imports and unused variables

Run pyflakes src/osmo_gsm_tester and then address the first
round of problems.

Change-Id: I02f1d89078dfdf37d53e2e20811bf36fb14ec3b0
diff --git a/src/osmo_gsm_tester/bts_nanobts.py b/src/osmo_gsm_tester/bts_nanobts.py
index a18f205..bec2433 100644
--- a/src/osmo_gsm_tester/bts_nanobts.py
+++ b/src/osmo_gsm_tester/bts_nanobts.py
@@ -18,11 +18,8 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import os
-import pprint
-import tempfile
 import re
-from abc import ABCMeta, abstractmethod
-from . import log, config, util, template, process, pcap_recorder, bts, pcu
+from . import log, config, util, process, pcap_recorder, bts, pcu
 from . import powersupply
 from .event_loop import MainLoop