Improve tests after removing deprecated textsize

[nulano]

For python-pillow#7059.

Changes proposed in this pull request:

• Instead of removing test for ImageDraw2.textsize, modify it for ImageDraw2.textbbox
• Remove duplicate asserts in test_imagefont:
  • "Check (w,h) of box a is (h,w) of box b" is included in "Check bbox b is (20, 20, 20 + h, 20 + w)"
  • "Check boxes a and b are same size" is included in "Check bbox b is (20, 20, 20 + w, 20 + h)"

[hugovk]

Thanks!

Remove duplicate asserts in test_imagefont:

• "Check (w,h) of box a is (h,w) of box b" is included in "Check bbox b is (20, 20, 20 + h, 20 + w)"
• "Check boxes a and b are same size" is included in "Check bbox b is (20, 20, 20 + w, 20 + h)"

The intent of "Check (w,h) of box a is (h,w) of box b" (-> "aha, so they must be the same but rotated") is much clearer than "Check bbox b is (20, 20, 20 + h, 20 + w)" -> ("hmm, where did these magic numbers come from? ah, okay, they're the original ones, plus we're calculating etc etc...").

So given a failure, I think the former is more readily debuggable. Can we remove the latter ones instead?

[radarhere]

I've included a version of this in python-pillow#7080