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/video_coding_impl.cc

@@ -270,10 +270,6 @@ class VideoCodingModuleImpl : public VideoCodingModule {
 };
 }  // namespace
 
-void VideoCodingModule::Codec(VideoCodecType codecType, VideoCodec* codec) {
-  VCMCodecDataBase::Codec(codecType, codec);
-}
-
 // DEPRECATED.  Create method for current interface, will be removed when the
 // new jitter buffer is in place.
 VideoCodingModule* VideoCodingModule::Create(Clock* clock,