Remove SSLMiddleware from oslo.config namespace

Change [1] removed SSLMiddleware from code but
missed removal of oslo-config namespace, this
patch cleans it up.

[1] https://review.openstack.org/#/c/506900/

Change-Id: Ibeeece25a13706e3ce0b58dbb9746090d881b909

config-generator.conf

@@ -9,7 +9,6 @@ namespace = heat.common.wsgi
 namespace = heat.engine.clients
 namespace = heat.engine.notification
 namespace = heat.engine.resources
-namespace = heat.api.middleware.ssl
 namespace = heat.api.aws.ec2token
 namespace = keystonemiddleware.auth_token
 namespace = oslo.messaging

setup.cfg

@@ -56,7 +56,6 @@ oslo.config.opts =
     heat.engine.clients = heat.engine.clients:list_opts
     heat.engine.notification = heat.engine.notification:list_opts
     heat.engine.resources = heat.engine.resources:list_opts
-    heat.api.middleware.ssl = heat.api.middleware.ssl:list_opts
     heat.api.aws.ec2token = heat.api.aws.ec2token:list_opts
     heat_integrationtests.common.config = heat_integrationtests.common.config:list_opts