Remove LibaomAv1EncoderIfSupported

Bug: webrtc:13573
Change-Id: Ia9a6d1809488d92753527350a61f0a46159ccd8b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/262814
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Xavier Lepaul‎ <xalep@webrtc.org>
Reviewed-by: Peter Hanspers <peterhanspers@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37033}

sdk/objc/api/video_codec/RTCVideoEncoderAV1.h

@@ -22,6 +22,4 @@ RTC_OBJC_EXPORT
  */
 + (id<RTC_OBJC_TYPE(RTCVideoEncoder)>)av1Encoder;
 
-+ (bool)isSupported;
-
 @end