Remove unused method term_handler

This method seems to be superseeded by exit_handler and grep tells me
it is unused.

Change-Id: I5a4dc126acbbe1ac2f99153bc7757c4f6e46fc8c
diff --git a/zuul/cmd/scheduler.py b/zuul/cmd/scheduler.py
index c3bfa5d..d94e9ea 100755
--- a/zuul/cmd/scheduler.py
+++ b/zuul/cmd/scheduler.py
@@ -67,10 +67,6 @@
         self.stop_gear_server()
         sys.exit(0)
 
-    def term_handler(self, signum, frame):
-        self.stop_gear_server()
-        os._exit(0)
-
     def start_gear_server(self):
         pipe_read, pipe_write = os.pipe()
         child_pid = os.fork()