gn2bp: Add an helper to drop unneeded third_party dependencies am: f5954480f5

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2469602

Change-Id: Ic1a2796c69f91fee88a90242904df9c6595a2756
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>