[impl_rabbit] Remove deprecated get_expiration method

This method is called on each message publishing and as shows
profiling (CProfile), the method is time-consuming, because it
uses pkg_resources module.

As we uses kombu>=3.0.25 since Mitaka, we no longer need in it.

Change-Id: I00723a3de81249946a8220ad47129f059d6d544f

oslo_messaging/_drivers/impl_rabbit.py

@@ -33,8 +33,6 @@ import kombu.messaging
 from oslo_config import cfg
 from oslo_log import log as logging
 from oslo_utils import netutils
-from oslo_utils import versionutils
-import pkg_resources
 import six
 from six.moves.urllib import parse
 
@@ -1143,18 +1141,6 @@ class Connection(object):
         with self._connection_lock:
             self.ensure(method, retry=retry, error_callback=_error_callback)
 
-    def _get_expiration(self, timeout):
-        # NOTE(gcb) kombu accept TTL as seconds instead of millisecond since
-        # version 3.0.25, so do conversion according to kombu version.
-        # TODO(gcb) remove this workaround when all supported branches
-        # with requirement kombu >=3.0.25
-        if timeout is not None:
-            kombu_version = pkg_resources.get_distribution('kombu').version
-            if not versionutils.is_compatible('3.0.25', kombu_version):
-                timeout = int(timeout * 1000)
-
-        return timeout
-
     def _publish(self, exchange, msg, routing_key=None, timeout=None):
         """Publish a message."""
 
@@ -1174,7 +1160,7 @@ class Connection(object):
             self._producer.publish(msg,
                                    exchange=exchange,
                                    routing_key=routing_key,
-                                   expiration=self._get_expiration(timeout),
+                                   expiration=timeout,
                                    compression=self.kombu_compression)
 
     def _publish_and_creates_default_queue(self, exchange, msg,