remove BpfInterfaceMapUpdater async update functionality

This is no longer needed due to being done synchronously via nativeRegisterIface()

Test: TreeHugger
  atest libnetworkstats_test
  atest NetworkStackIntegrationTests:android.net.NetworkStatsIntegrationTest
  atest FrameworksNetTests:android.net.connectivity.com.android.server.net.BpfInterfaceMapUpdaterTest
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I9c0c79d23657fb5cb5296fb918f76f1fc896baa1