GYP: Remove targets inside include_tests==1 that are converted to GN.

Remove a large number of targets that are no longer built, to reduce maintenance.
Only targets that have a GN version were removed.

BUG=webrtc:6323
NOTRY=True
NOPRESUBMIT=True

Review-Url: https://codereview.webrtc.org/2340773003
Cr-Commit-Position: refs/heads/master@{#14231}

webrtc/modules/audio_coding/codecs/opus/opus.gypi

@@ -50,24 +50,4 @@
       ],
     },
   ],
-  'conditions': [
-    ['include_tests==1', {
-      'targets': [
-        {
-          'target_name': 'webrtc_opus_fec_test',
-          'type': 'executable',
-          'dependencies': [
-            'webrtc_opus',
-            '<(webrtc_root)/base/base.gyp:rtc_base_approved',
-            '<(webrtc_root)/common_audio/common_audio.gyp:common_audio',
-            '<(webrtc_root)/test/test.gyp:test_support_main',
-            '<(DEPTH)/testing/gtest.gyp:gtest',
-          ],
-          'sources': [
-            'opus_fec_test.cc',
-          ],
-        },
-      ],
-    }],
-  ],
 }