Stop using _LE, make heat-engine not die in OpenStack Pike and later

"from heat.common.i18n import _LE" can't work in OpenStack releases
later than Ocata. Stop using it, and remove the import.

Fixes F5Networks#166 for Pike.

f5_heat/resources/f5_sys_iappservice.py

@@ -18,7 +18,6 @@
 
 from heat.common import exception
 from heat.common.i18n import _
-from heat.common.i18n import _LE
 from heat.engine import properties
 from heat.engine import resource
 
@@ -114,9 +113,7 @@ def _check_iapp_answers(self, prop_name):
                 self.properties[prop_name]
             )
         except Exception:
-            LOG.error(
-                _LE("'%s' property failed to parse as JSON") % prop_name
-            )
+            LOG.error("'%s' property failed to parse as JSON" % prop_name)
             raise
 
     def _build_service_dict(self):