Drop a half-uploaded take's server buffer when the user re-records.

Stored audio is left alone. A named take still uploading is also marked failed, so it no longer holds the row against the user's next take, and a part of it that arrives later is refused.

recording_id says which take to drop. Without it the row's current take is assumed, which is wrong as soon as a second tab has moved the row on: the caller would clear a buffer that is still being filled. Callers know their own id, so they send it.