C2 VTS: Enable AdaptiveBitrateTest only for CDD mandated encoders am: 15ccfa68a8 am: e5ac6fbdaa am: 3d74f2bde0 am: e20f78ca11

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/15898098

Change-Id: Ibcba2de886ea17a947dff20c1af20006b4024cae