Drop workarounds for PDFium's libpng

Drops workarounds for separating Chromium's and PDFium's copies of
libpng. PDFium no longer uses its own copy of libpng.

Fixed: 1130821
Change-Id: Ica77b4109448366b8711c4f649b287b362d3462b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4021576
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
Auto-Submit: K. Moon <kmoon@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1072225}
NOKEYCHECK=True
GitOrigin-RevId: e751ae0357beef85e5b18d0a2e741592ba1e8a43
4 files changed