test: remove necessity to call create_callback_map

Remove necessity to call create_callback_map (as well as the function
itself) from the Python P2P test framework. Invoke the appropriate
methods directly.

- Easy to forget to call it and wonder why it doesn't work
- Simplifies the code
- This makes it easier to handle new messages in subclasses

qa/rpc-tests/test_framework/comptool.py

@@ -45,7 +45,6 @@ class TestNode(NodeConnCB):
 
     def __init__(self, block_store, tx_store):
         NodeConnCB.__init__(self)
-        self.create_callback_map()
         self.conn = None
         self.bestblockhash = None
         self.block_store = block_store