Remove FrontSide audio from answer without requiring entire FrontSide by located.

This is a rather benign code change. Previously, code attempted to strip the entire part introduced by {{FrontSide}} from the answer, in an attempt to not play audio from the question, but as pointed out by Xiao, type answer prompts broke this. The break was due to the fact that the prompts from FrontSide content are transformed, so as not be literally found at the point we try to strip audio. This changes the code to only look for exactly the embedded sounds from FrontSide. It has been tested to work with type answer prompts.