Removing RTC_SUPPORTS_METAL compilation flag. This flag is a holdover from before either macOS or the iOS Simulator supported Metal rendering.

Bug: webrtc:12638
Change-Id: Iced21bfac40192f609b65f5ea1dc3393ee1695fb
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/222461
Commit-Queue: Jake Bromberg <jakebromberg@google.com>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Peter Hanspers <peterhanspers@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34347}

sdk/objc/components/renderer/metal/RTCMTLVideoView.h

@@ -21,8 +21,6 @@ NS_ASSUME_NONNULL_BEGIN
  *
  * It has id<RTCVideoRenderer> property that renders video frames in the view's
  * bounds using Metal.
- * NOTE: always check if metal is available on the running device via
- * RTC_SUPPORTS_METAL macro before initializing this class.
  */
 NS_CLASS_AVAILABLE_IOS(9)
 

sdk/objc/components/renderer/metal/RTCMTLVideoView.m

@@ -86,11 +86,7 @@
 #pragma mark - Private
 
 + (BOOL)isMetalAvailable {
-#if defined(RTC_SUPPORTS_METAL)
   return MTLCreateSystemDefaultDevice() != nil;
-#else
-  return NO;
-#endif
 }
 
 + (MTKView *)createMetalView:(CGRect)frame {