BPF: remove duplicate cflags and update btf flags. am: e0a0789c53

Original change: https://android-review.googlesource.com/c/platform/system/bpf/+/3195892

Change-Id: I353b90aec5269d6c1f8abaac8d2ccb90cfb02939
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>