Remove all references to GYP

Remove all .gyp and .gypi files.
Remove entries from OWNERS files for *.isolate, *.gyp, *.gypi
Remove unused scripts in webrtc/build.

BUG=webrtc:6323
R=henrika@webrtc.org, phoglund@webrtc.org

Review URL: https://codereview.webrtc.org/2509703002 .

Cr-Commit-Position: refs/heads/master@{#15107}

webrtc/modules/video_coding/codecs/tools/OWNERS

@@ -1,5 +0,0 @@
-
-# These are for the common case of adding or renaming files. If you're doing
-# structural changes, please get a review from a reviewer in this file.
-per-file *.gyp=*
-per-file *.gypi=*

webrtc/modules/video_coding/codecs/tools/video_codecs_tools.gypi

@@ -1,36 +0,0 @@
-# Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
-#
-# Use of this source code is governed by a BSD-style license
-# that can be found in the LICENSE file in the root of the source
-# tree. An additional intellectual property rights grant can be found
-# in the file PATENTS.  All contributing project authors may
-# be found in the AUTHORS file in the root of the source tree.
-
-{
-  'conditions': [
-    ['include_tests==1', {
-      'targets': [
-        {
-          'target_name': 'video_quality_measurement',
-          'type': 'executable',
-          'dependencies': [
-            'video_codecs_test_framework',
-            'webrtc_video_coding',
-            '<(DEPTH)/third_party/gflags/gflags.gyp:gflags',
-            '<(webrtc_root)/common.gyp:webrtc_common',
-            '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers_default',
-            '<(webrtc_root)/test/test.gyp:test_support',
-            '<(webrtc_vp8_dir)/vp8.gyp:webrtc_vp8',
-          ],
-          'sources': [
-            'video_quality_measurement.cc',
-          ],
-          # Disable warnings to enable Win64 build, issue 1323.
-          'msvs_disabled_warnings': [
-            4267,  # size_t to int truncation.
-          ],
-        },
-      ], # targets
-    }], # include_tests
-  ], # conditions
-}