Remove early size check requirement in OffByTwo.kt

This will make `OffByTwo.kt` behaves identical to the original `PixelPerfect` differ.
But most importantly, it will restore the initial behavior of `ImageUtils.assertImageSimilar()` itself, checking for differences in size and correctly producing the expected delta (and actual) images in case of a size mismatch.

Relates to cashapp#1716

paparazzi/src/main/java/app/cash/paparazzi/internal/OffByTwo.kt

@@ -8,8 +8,6 @@ import kotlin.math.max
 
 internal object OffByTwo : Differ {
   override fun compare(expected: BufferedImage, actual: BufferedImage): DiffResult {
-    check(expected.width == actual.width && expected.height == actual.height) { "Images are different sizes" }
-
     val expectedWidth = expected.width
     val expectedHeight = expected.height