bug#70093: Remove unnecessary `image-tests--map-equal'

[Joseph Turner]

With the resolution of bug#69992, it may be possible to remove the
`image-tests--map-equal' equality predicate from lisp/image-tests.el.

Eli and David, would you please apply the attached patch and then run
the tests to see if we still need to allow for tolerances in
`image--compute-map-and-original-map'?

The tests pass for me, but then again, they never failed on my machine...

Thank you!! I'm grateful for this fun collaboration. :)

Joseph