This reverts commit 30e23517.

Reason for revert: This script turned animated PNGs for ChromeOS into flat PNGs. Scary!

Original change's description:
> Run tools/resources/optimize-png-files.sh
>
> Optimizes a significant number of .png files and cuts ~3.6M in total.
>
> Bug: None
> Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
> Change-Id: I53a951a6410839c3b21f7155f22e2fedb3fb963f
> Reviewed-on: https://chromium-review.googlesource.com/1012263
> Reviewed-by: Scott Violet <sky@chromium.org>
> Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
> Commit-Queue: Peter Boström <pbos@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#551066}

TBR=sky@chromium.org,bauerb@chromium.org,pbos@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:835197
Change-Id: I4852e2ee84ac51ffb765649ff838c03dfba564d3
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Reviewed-on: https://chromium-review.googlesource.com/1028336
Commit-Queue: Peter Boström <pbos@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553826}