Cleaned up references to executor specific RPCServer types

In oslo.messaging design phase, it was planned to introduce executor
specific RPCServer types though they were never implemented. References
to those types sneaked into docstrings from the original design
document. Since we're not going to implement those types now, docstrings
should be updated accordingly.

Change-Id: Ic4017bb8f89d47115bb7dc59483e81d26c76212b

oslo/messaging/rpc/server.py

@@ -40,9 +40,6 @@ RPC servers have start(), stop() and wait() messages to begin handling
 requests, stop handling requests and wait for all in-process requests to
 complete.
 
-An RPC server class is provided for each supported I/O handling framework.
-Currently BlockingRPCServer and eventlet.RPCServer are available.
-
 A simple example of an RPC server with multiple endpoints might be::
 
     from oslo.config import cfg
@@ -70,7 +67,8 @@ A simple example of an RPC server with multiple endpoints might be::
         ServerControlEndpoint(self),
         TestEndpoint(),
     ]
-    server = messaging.get_rpc_server(transport, target, endpoints)
+    server = messaging.get_rpc_server(transport, target, endpoints,
+                                      executor='eventlet')
     server.start()
     server.wait()
 

oslo/messaging/server.py

@@ -107,9 +107,7 @@ class MessageHandlingServer(object):
         process, thread or co-operatively scheduled coroutine or simply by
         registering a callback with an event loop. Similarly, the executor may
         choose to dispatch messages in a new thread, coroutine or simply the
-        current thread. An RPCServer subclass is available for each I/O
-        strategy supported by the library, so choose the subclass appropriate
-        for your program.
+        current thread.
         """
         if self._executor is not None:
             return