Delete all remaining callers of iptables.

Also move to binder_test.cpp some string constants that are used
only there.

(cherry picked from commit 5c68b9c1)

Bug: 28362720
Test: bullhead builds,boots
Test: netd_{unit,integration}_test pass
Change-Id: Icebaac93fc3a661902deced985119d2d1735732e
Merged-In: I3f72946de374a7deaeef88b1dd5589d9a20ccce7