Revert "examples/text: Use golang.org/x/image/font/opentype"
Revert "examples/text: Use golang.org/x/image/font/opentype"

This reverts commit 013a42ddb88dbacdb1398c8d81e1bcb560f7781d.

Reason: #1377

hajimehoshi/ebiten,hajimehoshi/ebiten