Remove slow tag from test_minbw test

test_qos_min_bw_allocation_basic usually execute in less than 60 secs,
so let's remove slow tag from it.
This patch removes the following config options from tempest-slow job:
* bridge_mappings and resource_provider_bandwidths from
neutron_core_plugin_conf
* qos_placement_physnet from network-feature-enabled in tempest.conf

Change-Id: I03c97edb9d7a177f5face046d1c9f60e4f1eeefa

tempest/scenario/test_minbw_allocation_placement.py

@@ -173,7 +173,6 @@ class MinBwAllocationPlacementTest(manager.NetworkScenarioTest):
                          port['port']['binding:profile']['allocation'])
 
     @decorators.idempotent_id('78625d92-212c-400e-8695-dd51706858b8')
-    @decorators.attr(type='slow')
     @utils.services('compute', 'network')
     def test_qos_min_bw_allocation_basic(self):
         """"Basic scenario with QoS min bw allocation in placement.

zuul.d/integrated-gate.yaml

@@ -300,16 +300,6 @@
       devstack_services:
         neutron-placement: true
         neutron-qos: true
-      devstack_local_conf:
-        post-config:
-          "/$NEUTRON_CORE_PLUGIN_CONF":
-            ovs:
-              bridge_mappings: public:br-ex
-              resource_provider_bandwidths: br-ex:1000000:1000000
-        test-config:
-          $TEMPEST_CONFIG:
-            network-feature-enabled:
-              qos_placement_physnet: public
       tempest_concurrency: 2
     group-vars:
       # NOTE(mriedem): The ENABLE_VOLUME_MULTIATTACH variable is used on both