Remove autolayout in RTCMTLVideoView.

Using layoutSubviews is a simpler solution to achieveing the desired
effect. Plus this will get rid of warrnings on iOS 11

Bug: webrtc:8467
Change-Id: Idaa041b7a0ed889905d97f645408fb3437154e73
Reviewed-on: https://webrtc-review.googlesource.com/17380
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Peter Hanspers <peterhanspers@webrtc.org>
Commit-Queue: Daniela Jovanoska Petrenko <denicija@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20523}
diff --git a/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m b/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m
index e36cb3a..48c3f33 100644
--- a/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m
+++ b/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m
@@ -91,15 +91,16 @@
     _metalView.delegate = self;
     [self addSubview:_metalView];
     _metalView.contentMode = UIViewContentModeScaleAspectFit;
-    _metalView.translatesAutoresizingMaskIntoConstraints = NO;
-    UILayoutGuide *margins = self.layoutMarginsGuide;
-    [_metalView.topAnchor constraintEqualToAnchor:margins.topAnchor].active = YES;
-    [_metalView.bottomAnchor constraintEqualToAnchor:margins.bottomAnchor].active = YES;
-    [_metalView.leftAnchor constraintEqualToAnchor:margins.leftAnchor].active = YES;
-    [_metalView.rightAnchor constraintEqualToAnchor:margins.rightAnchor].active = YES;
   }
 }
 
+#pragma mark - Private
+
+- (void)layoutSubviews {
+  [super layoutSubviews];
+  _metalView.frame = self.bounds;
+}
+
 #pragma mark - MTKViewDelegate methods
 
 - (void)drawInMTKView:(nonnull MTKView *)view {