rename InterfaceMapUpdater to InterfaceMapHelper

since it doesn't actually update any more...

Done via:
  git grep InterfaceMapUpdater | cut -d: -f1 | sort -u | while read i; do sed -i -r 's@InterfaceMapUpdater@InterfaceMapHelper@g' "$i"; done
  git mv ./tests/unit/java/com/android/server/net/BpfInterfaceMapUpdaterTest.java ./tests/unit/java/com/android/server/net/BpfInterfaceMapHelperTest.java
  git mv ./service-t/src/com/android/server/net/BpfInterfaceMapUpdater.java ./service-t/src/com/android/server/net/BpfInterfaceMapHelper.java

Test: TreeHugger
  atest libnetworkstats_test
  atest FrameworksNetTests:android.net.connectivity.com.android.server.net.BpfInterfaceMapHelperTest
  atest NetworkStackIntegrationTests:android.net.NetworkStatsIntegrationTest
  atest --iterations=100 NetworkStackIntegrationTests:android.net.NetworkStatsIntegrationTest
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I07b57158347757f3f8dc4f24803a9bbf30445f7d