serializer: deprecate RequestContextSerializer

The plan is still to remove it to avoid any dependency on oslo.context.

Change-Id: I9fc982c89f537b385dda37800fe46b086eb4daf6

oslo_messaging/serializer.py

@@ -19,6 +19,7 @@ __all__ = ['Serializer', 'NoOpSerializer', 'JsonPayloadSerializer',
 
 import abc
 
+from debtcollector import removals
 from oslo_context import context as common_context
 from oslo_serialization import jsonutils
 import six
@@ -63,6 +64,9 @@ class Serializer(object):
         """
 
 
+@removals.removed_class("RequestContextSerializer",
+                        version="4.6",
+                        removal_version="5.0")
 class RequestContextSerializer(Serializer):
 
     def __init__(self, base):