pySim-shell.py: remove unused imports of 'bg' from 'cmd2'

Change-Id: Ic2a73a98f322be391e54215bc5fc3358776da0ae
diff --git a/pySim-shell.py b/pySim-shell.py
index e52c4ef..33332a2 100755
--- a/pySim-shell.py
+++ b/pySim-shell.py
@@ -23,7 +23,7 @@
 import traceback
 
 import cmd2
-from cmd2 import style, fg, bg
+from cmd2 import style, fg
 from cmd2 import CommandSet, with_default_category, with_argparser
 import argparse