Make the verifier a thread job instead of a thread

The verifier, like the synchronizer, now runs as part of the
network proxy thread.

lib/network_proxy.py

@@ -66,7 +66,7 @@ class NetworkProxy(util.DaemonThread):
 
     def run(self):
         while self.is_running():
-            self.run_jobs()    # Synchronizer, for now
+            self.run_jobs()    # Synchronizer and Verifier
             try:
                 response = self.pipe.get()
             except util.timeout:
@@ -185,9 +185,6 @@ class NetworkProxy(util.DaemonThread):
     def get_interfaces(self):
         return self.interfaces
 
-    def get_header(self, height):
-        return self.synchronous_get([('network.get_header', [height])])[0]
-
     def get_local_height(self):
         return self.blockchain_height