Remove {media,p2p,pc,xmllite,xmpp}_tests.gypi files.

webrtc/media/rtc_media_unittests.isolate

 # Copyright (c) 2016 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': [
     ['OS=="linux" or OS=="mac" or OS=="win"', {
       'variables': {
         'command': [
           '<(PRODUCT_DIR)/rtc_media_unittests<(EXECUTABLE_SUFFIX)',
         ],
         'files': [
           '<(PRODUCT_DIR)/rtc_media_unittests<(EXECUTABLE_SUFFIX)',
           '<(DEPTH)/resources/media/captured-320x240-2s-48.frames',
           '<(DEPTH)/resources/media/faces.1280x720_P420.yuv',
           '<(DEPTH)/resources/media/faces_I420.jpg',
           '<(DEPTH)/resources/media/faces_I422.jpg',
           '<(DEPTH)/resources/media/faces_I444.jpg',
           '<(DEPTH)/resources/media/faces_I411.jpg',
           '<(DEPTH)/resources/media/faces_I400.jpg',
         ],
       },
     }],
   ],
 }