Revert "libpng: Upgrade to 1.6.26"

This reverts commit 3586ba4f3287ed6a9e6e15b01b717e2cf1bd8647.

https://b.corp.google.com/u/1/issues/33057876

Change-Id: I2c0ea5e3feba74f70009d6ccda4e43b32a17b832
64 files changed