libvlc: gdb: fix script

- Fix the ANDROID_MANIFEST path (app/build instead of vlc-android/build).
- Remove useless copies (libs folder, Android.mk, whole obj/local/*/ when only
  the so are needed)
- Configure it only for the arch of the last built APK. This fixes armv7 builds
  that could not be debugged on armv8 arches.