Replace VideoCaptureDataCallback by VideoSinkInterface.

This also deletes unused features of the video_capturer interface, the classes
VideoCaptureFeedBack, VideoCaptureEncodeInterface and related methods,
and the module id which used to be passed as an argument to the
VideoCaptureDataCallback.

In theory the module id could have been used to let a single
VideoCaptureDataCallback serve several capturers, and demultiplex
on the id, but in practice, it was unused. With this change, it is
required to use a separate VideoSinkInterface for each capturer.

BUG=webrtc:6789

Review-Url: https://codereview.webrtc.org/2534553002
Cr-Commit-Position: refs/heads/master@{#15540}

webrtc/modules/video_capture/linux/video_capture_linux.h

@@ -25,7 +25,7 @@ namespace videocapturemodule
 class VideoCaptureModuleV4L2: public VideoCaptureImpl
 {
 public:
-    VideoCaptureModuleV4L2(int32_t id);
+    VideoCaptureModuleV4L2();
     virtual ~VideoCaptureModuleV4L2();
     virtual int32_t Init(const char* deviceUniqueId);
     virtual int32_t StartCapture(const VideoCaptureCapability& capability);