DO NOT MERGE: NatController: remove flushing the INPUT/OUTPUT tables.

DO NOT MERGE: cherry-pick from master, as oem's will be updating this
file in HC.

It doesn't use them, so it should not have to flush them.
This is a minimalistic attempt to cooperate with the BandwidthController.

Change-Id: Ia175a86403adf034ac6f44d7ebc4ebe941881368