Removed redundant condition in CallAudioProvider.pullAudio

- Note that the condition only matters when eadAtHead != null
- Also note that audioFrames never contains a null EncodedAudioData (addFrame is only called from one place, which derefs the EncodedAudioData just before calling addFrame)
- eadHead is a specific value in audioFrames, but ead is any value
- Therefore eadHead != null implies ead != null
- Therefore ead == null is false, and only the right side of the || matters.