Make code looks more python after review

Author: Zhen

neo4j/bolt/connection.py

@@ -508,7 +508,7 @@ def deactivate(self, address):
                         conn.close()
                     except IOError:
                         pass
-            if len(connections) == 0:
+            if not connections:
                 self.remove(address)
 
     def remove(self, address):

neo4j/v1/routing.py

@@ -81,9 +81,6 @@ def replace(self, elements=()):
         e.clear()
         e.update(OrderedDict.fromkeys(elements))
 
-    def elements(self):
-        return list(self._elements)
-
 
 class RoutingTable(object):
 
@@ -144,7 +141,7 @@ def update(self, new_routing_table):
         self.ttl = new_routing_table.ttl
 
     def servers(self):
-        return set(self.routers.elements() + self.writers.elements() + self.readers.elements())
+        return set(self.routers) | set(self.writers) | set(self.readers)
 
 
 class RoutingSession(BoltSession):