[gold] imgloader_test.go: Stop conflating digests and MD5 hashes for test PNG images.
[gold] imgloader_test.go: Stop conflating digests and MD5 hashes for test PNG images.

This CL aims to address some of the comments in https://skia-review.googlesource.com/c/buildbot/+/245375, where it's pointed out that conflating image digests and MD5 hashes of the images is misleading and does not represent what happens in practice.


Bug: skia:9483
Change-Id: Iaea5d2a8e9f1aedcd8aaef33a161f556f02539e7
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/245587
Auto-Submit: Leandro Lovisolo <f558143c2568be8d55575d13f30a1fc5cb8009d5@google.com>
Commit-Queue: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>
Reviewed-by: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>

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