Fix -Wextra-semi warnings.

Starting from https://chromium-review.googlesource.com/c/1485012,
-Wextra-semi is enabled and WebRTC has some violations to fix.

This is a follow-up of https://webrtc-review.googlesource.com/c/123560.

Bug: webrtc:10355
Change-Id: I012b7497fc8991037fd77aa98f1579c22e08206f
Reviewed-on: https://webrtc-review.googlesource.com/c/124126
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26831}

api/test/fake_media_transport.h

@@ -44,7 +44,7 @@ class FakeMediaTransport : public MediaTransportInterface {
 
   RTCError RequestKeyFrame(uint64_t channel_id) override {
     return RTCError::OK();
-  };
+  }
 
   void SetReceiveAudioSink(MediaTransportAudioSinkInterface* sink) override {}
   void SetReceiveVideoSink(MediaTransportVideoSinkInterface* sink) override {}