Remove remaining quality-analysis (QM).

This was never turned on, contains a lot of complexity and somehow
manages triggering a bug in a downstream project.

BUG=webrtc:5066
R=marpan@webrtc.org
TBR=mflodman@webrtc.org

Review URL: https://codereview.webrtc.org/1917323002 .

Cr-Commit-Position: refs/heads/master@{#12692}

webrtc/modules/video_coding/video_coding.gypi

@@ -28,7 +28,6 @@
         # headers
         'codec_database.h',
         'codec_timer.h',
-        'content_metrics_processing.h',
         'decoding_state.h',
         'encoded_frame.h',
         'fec_tables_xor.h',
@@ -49,8 +48,6 @@
         'packet.h',
         'packet_buffer.h',
         'percentile_filter.h',
-        'qm_select_data.h',
-        'qm_select.h',
         'receiver.h',
         'rtt_filter.h',
         'session_info.h',
@@ -61,7 +58,6 @@
         # sources
         'codec_database.cc',
         'codec_timer.cc',
-        'content_metrics_processing.cc',
         'decoding_state.cc',
         'encoded_frame.cc',
         'frame_buffer.cc',
@@ -78,7 +74,6 @@
         'packet.cc',
         'packet_buffer.cc',
         'percentile_filter.cc',
-        'qm_select.cc',
         'receiver.cc',
         'rtt_filter.cc',
         'session_info.cc',