Delete dead code for video quality calculation.

Previously, the only user of this code was the
VideoProcessorIntegrationTest. We have now changed that
test to directly calculate image quality metrics using libyuv,
similar to how the full stack tests and browser tests work.

Bug: webrtc:8448
Change-Id: Ia7a607d7ddc37741fba76d56aa7297851ffa1c6b
Reviewed-on: https://webrtc-review.googlesource.com/43760
Commit-Queue: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22341}

modules/video_coding/codecs/test/videoprocessor_integrationtest.cc

@@ -36,7 +36,6 @@
 #include "rtc_base/ptr_util.h"
 #include "system_wrappers/include/sleep.h"
 #include "test/testsupport/fileutils.h"
-#include "test/testsupport/metrics/video_metrics.h"
 
 namespace webrtc {
 namespace test {