pngcrush: New upstream package, 1.7.81

Upgraded media-gfx/pngcrush to version 1.7.81 on amd64. This is inteded
to be used on the host only.

This patch relaxes the dependency on libpng to use the version we have
in chromiumos-overlay since the new version is not required and was
also relaxed upstream in a later version of pngcrush.

BUG=chromium:465647
TEST=sudo emerge pngcrush
TEST=Ran pngcrush on the initramfs images.

Original-Change-Id: I7b6c6f0e65ccf05e315715e714a450ec34e78965
Original-Reviewed-on: https://chromium-review.googlesource.com/259917
Trybot-Ready: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
(cherry picked from commit e2094d4d2be5a8dfc8f8bc669c24faabfade30a4)

Change-Id: Iaccd9703d42f9d92b96a68861c10801471b05a57
Reviewed-on: https://chromium-review.googlesource.com/262049
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Hung-Te Lin <hungte@chromium.org>
Tested-by: Hung-Te Lin <hungte@chromium.org>
4 files changed