bpo-43013: Update idlelib code to 3.x  (GH-24315)

Remove 9 remaining '(object)' occurrences in class headers in idlelib
and 25 '()' occurrences in idlelib.idle_test class headers.
diff --git a/Lib/idlelib/rpc.py b/Lib/idlelib/rpc.py
index aa8cbd3..8efcf04 100644
--- a/Lib/idlelib/rpc.py
+++ b/Lib/idlelib/rpc.py
@@ -125,7 +125,7 @@ def handle_error(self, request, client_address):
 response_queue = queue.Queue(0)
 
 
-class SocketIO(object):
+class SocketIO:
 
     nextseq = 0
 
@@ -486,7 +486,7 @@ def EOFhook(self):
 
 #----------------- end class SocketIO --------------------
 
-class RemoteObject(object):
+class RemoteObject:
     # Token mix-in class
     pass
 
@@ -497,7 +497,7 @@ def remoteref(obj):
     return RemoteProxy(oid)
 
 
-class RemoteProxy(object):
+class RemoteProxy:
 
     def __init__(self, oid):
         self.oid = oid
@@ -547,7 +547,7 @@ def get_remote_proxy(self, oid):
         return RPCProxy(self, oid)
 
 
-class RPCProxy(object):
+class RPCProxy:
 
     __methods = None
     __attributes = None
@@ -596,7 +596,7 @@ def _getattributes(obj, attributes):
             attributes[name] = 1
 
 
-class MethodProxy(object):
+class MethodProxy:
 
     def __init__(self, sockio, oid, name):
         self.sockio = sockio