Make exoplayer not depend statically on androidx am: 351f998ce9

Original change: https://android-review.googlesource.com/c/platform/external/exoplayer/+/2073974

Change-Id: I346837773f68128f1628c3d9859a97403c25eaba
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>