Use only treble property in the cuttlefish rild

When full treble is enabled in newer platform versions, it is no longer
possible to use rild.libpath; we must use vendor.rild.libpath instead.

As using this property works for old platform versions too, just
unconditionally enable use of the new property name.

Bug: 129163131
Change-Id: I41ef3f32dfaa93d2666338109b7e5d1c0f8ccf10