Bug 1353607. P7 - remove the unused function. r=kikuo

MozReview-Commit-ID: AWf7ritkbJ5

--HG--
extra : rebase_source : f0d1bc3737f5bdd0ebe67aaa0440da4d4dcb81c4
extra : intermediate-source : a1988b5e24c807885719330e00d0ee53541ad5ea
extra : source : b87cf11a3235a6cb5f3369f6fbf8a6bdf7f5d005

dom/media/MediaDecoderStateMachine.cpp

@@ -144,11 +144,6 @@ static_assert(LOW_BUFFER_THRESHOLD_USECS > AMPLE_AUDIO_USECS,
 // Amount of excess usecs of data to add in to the "should we buffer" calculation.
 static const uint32_t EXHAUSTED_DATA_MARGIN_USECS = 100000;
 
-static int64_t DurationToUsecs(TimeDuration aDuration)
-{
-  return static_cast<int64_t>(aDuration.ToSeconds() * USECS_PER_S);
-}
-
 static const uint32_t MIN_VIDEO_QUEUE_SIZE = 3;
 static const uint32_t MAX_VIDEO_QUEUE_SIZE = 10;
 #ifdef MOZ_APPLEMEDIA