Bug 1417660 - Remove duplicate native_window.h in system-headers.mozbuild; r=chmanchester

MozReview-Commit-ID: 3ltJ9kEXYsj

--HG--
extra : rebase_source : 641d7702e43695b4ff36403247ed367d8cebfc99

config/system-headers.mozbuild

@@ -1055,7 +1055,6 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'android':
         'android/log.h',
         'android/looper.h',
         'android/native_window.h',
-        'android/native_window.h',
         'android/native_window_jni.h',
         'audio_effects/effect_aec.h',
         'audio_effects/effect_ns.h',