Disable encoder scaling on iPhone4S.

Scaling causes us to work the CPU too much, which very quickly degrades quality. This causes us to at least behave better on good networks.

NOTRY=True
BUG=

Review-Url: https://codereview.webrtc.org/2205763002
Cr-Commit-Position: refs/heads/master@{#13630}

webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm

@@ -582,6 +582,7 @@ AVFoundationVideoCapturer::AVFoundationVideoCapturer()
 #if TARGET_OS_IPHONE
   if ([UIDevice deviceType] == RTCDeviceTypeIPhone4S) {
     supported_formats.push_back(cricket::VideoFormat(kIPhone4SFormat));
+    set_enable_video_adapter(false);
   } else {
     supported_formats.push_back(cricket::VideoFormat(kDefaultFormat));
   }