Drop support for playing output through aplay in intelligibility_proc

It was hardly used, making the code more complex than needed and caused problems on iOS because it uses system.

BUG=webrtc:5549
R=kjellander@webrtc.org

Review URL: https://codereview.webrtc.org/1708353002 .

Cr-Commit-Position: refs/heads/master@{#11677}

webrtc/modules/audio_processing/audio_processing_tests.gypi

@@ -72,18 +72,6 @@
       'sources': [
         'intelligibility/test/intelligibility_proc.cc',
       ],
-      'conditions': [
-        ['OS=="ios"', {
-          'xcode_settings': {
-            'WARNING_CFLAGS':  [
-              # Suppress compiler warnings about deprecated that triggered
-              # when moving from ios_deployment_target 7.0 to 9.0.
-              # See webrtc:5549 for more details.
-              '-Wno-deprecated-declarations',
-            ],
-          },
-        }],
-      ],
     }, # intelligibility_proc
   ],
   'conditions': [