Replaces OS_ANDROID with WEBRTC_ANDROID to disable ProcessNoLossChangeFrameRateFrameDropVP9 on Android. BUG=webrtc:6057 R=danilchap@webrtc.org TBR=phoglund@webrtc.org Review URL: https://codereview.webrtc.org/2101673002 . Cr-Commit-Position: refs/heads/master@{#13300}