remove useless log message

When we calculate statistic data from database, we print a debug
level log which says something like:

computed value coming from u'(<ceilometer.storage.impl_mongodb.Connection
object at 0x12345678>,)'

This message only indicates which type of database we are using,
nothing more. However the database type is specified by config file,
so this log is actually redundant.

Change-Id: Ia52f2d5f74509999097151e6906b4233214d74eb
Closes-Bug: #1459911

ceilometer/api/controllers/v2/meters.py

@@ -403,9 +403,6 @@ class MeterController(rest.RestController):
         try:
             computed = pecan.request.storage_conn.get_meter_statistics(
                 f, period, g, aggregate)
-            LOG.debug(_('computed value coming from %r'),
-                      pecan.request.storage_conn)
-
             return [Statistics(start_timestamp=start,
                                end_timestamp=end,
                                **c.as_dict())