Remove duplicate method definitions in NodeConnCB subclasses

All Node classes in individual test cases subclass from NodeConnCB. Many
have duplicate definitions for methods that are defined in the base
class. This commit removes those duplicate definitions.

This commit removes ~290 lines of duplicate code.

test/functional/p2p-timeouts.py

@@ -28,20 +28,9 @@ from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import *
 
 class TestNode(NodeConnCB):
-    def __init__(self):
-        super().__init__()
-        self.connected = False
-        self.received_version = False
-
-    def on_open(self, conn):
-        self.connected = True
-
-    def on_close(self, conn):
-        self.connected = False
-
     def on_version(self, conn, message):
         # Don't send a verack in response
-        self.received_version = True
+        pass
 
 class TimeoutsTest(BitcoinTestFramework):
     def __init__(self):
@@ -83,7 +72,7 @@ class TimeoutsTest(BitcoinTestFramework):
 
         sleep(30)
 
-        assert(self.no_verack_node.received_version)
+        assert "version" in self.no_verack_node.last_message
 
         assert(self.no_verack_node.connected)
         assert(self.no_version_node.connected)