Revert "internal/mipmap: bug fix: do not consider filter to determine mipmap level"
Revert "internal/mipmap: bug fix: do not consider filter to determine mipmap level"

This reverts commit 42833614fb6f24e5daa829df47f446fcd0f970ac.

Reason: test failure: TestImageEdge

hajimehoshi/ebiten,hajimehoshi/ebiten