Fix typing error in forwarder.py.

This wasn't triggered earlier since this function is not used upstream.

TBR=bulach@chromium.org
BUG=242846

Review URL: https://codereview.chromium.org/21839003

git-svn-id: http://src.chromium.org/svn/trunk/src/build@215287 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/pylib/forwarder.py

@@ -139,7 +139,7 @@ class Forwarder(object):
       port_map = Forwarder._GetInstanceLocked(
           None, None)._device_to_host_port_map
       adb_serial = adb.Adb().GetSerialNumber()
-      for ((device_serial, device_port), _) in port_map:
+      for (device_serial, device_port) in port_map.keys():
         if adb_serial == device_serial:
           Forwarder._UnmapDevicePortLocked(device_port, adb)