Removing VCMCodecDataBase::Codec and VideoCodingModule::Codec.

This CL brings us one step closer to removing CodecDatabase and
GenericEncoder, by removing the static VCM::Codec(). Codec specific
methods are moved to video_encoder.cc (they already belonged to this
class) and getting default generic codec settings has been moved to a
test specific file.

This CL also makes video_encoder.h pass style guide and lint checks,
since these checks are triggered with the new video_encoder.cc file.

BUG=webrtc:8064

Review-Url: https://codereview.webrtc.org/2993923002
Cr-Commit-Position: refs/heads/master@{#19303}

webrtc/modules/video_coding/codec_database.h

@@ -47,10 +47,6 @@ class VCMCodecDataBase {
   explicit VCMCodecDataBase(VCMEncodedFrameCallback* encoded_frame_callback);
   ~VCMCodecDataBase();
 
-  // Sender Side
-  // Returns the default settings for the codec with type |codec_type|.
-  static void Codec(VideoCodecType codec_type, VideoCodec* settings);
-
   // Sets the sender side codec and initiates the desired codec given the
   // VideoCodec struct.
   // Returns true if the codec was successfully registered, false otherwise.