Per-layer frame dropping was recently implemented in VP9 SVC encoder and set as default mode. This disables per-layer frame dropping in WebRTC VP9 encoder wrapper since receiver (jitter buffer) can't handle such drops yet. Bug: none Change-Id: Iad5491abf1e3fc1bccfe44eb7276ff6363176029 Reviewed-on: https://webrtc-review.googlesource.com/66460 Reviewed-by: Marco Paniconi <marpan@google.com> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org> Commit-Queue: Sergey Silkin <ssilkin@webrtc.org> Cr-Commit-Position: refs/heads/master@{#22721}