Sever the forward reference from connections to their users

This will make it easier to keep connections around while the
data structures that use them change (eg, during a reload).

Change-Id: I465e1ca3c44ca263047f89d84197b5cf514bdfa3

zuul/connection/__init__.py

@@ -43,14 +43,6 @@ class BaseConnection(object):
         self.connection_name = connection_name
         self.connection_config = connection_config
 
-        # Keep track of the sources, triggers and reporters using this
-        # connection
-        self.attached_to = {
-            'source': [],
-            'trigger': [],
-            'reporter': [],
-        }
-
     def onLoad(self):
         pass
 
@@ -60,9 +52,6 @@ class BaseConnection(object):
     def registerScheduler(self, sched):
         self.sched = sched
 
-    def registerUse(self, what, instance):
-        self.attached_to[what].append(instance)
-
     def maintainCache(self, relevant):
         """Make cache contain relevant changes.
 

zuul/lib/connections.py

@@ -118,9 +118,6 @@ class ConnectionRegistry(object):
                 driver_config, self.sched, connection
         )
 
-        if connection:
-            connection.registerUse(dtype, driver_instance)
-
         return driver_instance
 
     def getSource(self, connection_name):