Revert "audio/wav: Allow passing non-io.Seeker to Decode"
Revert "audio/wav: Allow passing non-io.Seeker to Decode"

This reverts commit 19cd69da5504aebea73f2fd00c7bf38b92d95dad.

Reason: Marked #1202 'won't fix'

hajimehoshi/ebiten,hajimehoshi/ebiten