Revert "Limit audio buffer to 700ms.  This prevents the frontend locking up when trying to stop playing an audio-only stream (e.g. DVB radio).  Without this patch the buffer tends to fill to around the 1500ms, which is below the current 2000ms limit, and AvFormatDecoder never leaves GetFrame."

This reverts commit f54d2672f224ba24224c8edd12fb0318797b3425.

Limiting the audio buffer to 700ms causes A/V sync issues for some people so reverting it until a better solution can be found.