Remove unused codes that was used in setChildChain

Previous commit update BpfNetMaps#setChildChain to use Java BpfMap.
This commit remove the code that is no longer used due to the previous
commit.

Bug: 217624062
Test: atest BpfNetMapsTest android.net.cts.ConnectivityManagerTest#testFirewallBlocking
Change-Id: I02656096c8752daf20d3578f209778c5adae9b0c
4 files changed