Remove native code path in BpfNetMaps.java

BpfNetMaps uses java library for updating bpf map as the default code
path.
This is already released to 100% production without any issues.
So this CL removes the old code path from BpfNetMaps.

Note that native_init only opens the bpf maps if sEnableJavaBpfMap is
true.
But if sEnableJavaBpfMap is true, no native code in TrafficController
access the bpf map.
So this CL can remove native_init.

Following CL will remove the nativce codes for old code path.

Bug: 217624062
Test: NetworkStaticLibsTests
Change-Id: Ifba198d9e6f93b53fd1dbf3b2aafb644da0b147d