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/codecs/tools/video_quality_measurement.cc

@@ -31,6 +31,7 @@
 #include "webrtc/test/testsupport/frame_writer.h"
 #include "webrtc/test/testsupport/metrics/video_metrics.h"
 #include "webrtc/test/testsupport/packet_reader.h"
+#include "webrtc/test/video_codec_settings.h"
 
 DEFINE_string(test_name, "Quality test", "The name of the test to run. ");
 DEFINE_string(test_description,
@@ -204,8 +205,7 @@ int HandleCommandLineFlags(webrtc::test::TestConfig* config) {
   config->use_single_core = FLAGS_use_single_core;
 
   // Get codec specific configuration.
-  webrtc::VideoCodingModule::Codec(webrtc::kVideoCodecVP8,
-                                   &config->codec_settings);
+  webrtc::test::CodecSettings(webrtc::kVideoCodecVP8, &config->codec_settings);
 
   // Check the temporal layers.
   if (FLAGS_temporal_layers < 0 ||