Don't use NEON optimized code in lpng_v163

The source files required to use the NEON function are not
included so we should not try to reference those symbols.

BUG=477162
TEST=ninja -C out_arm/Release/ pdfium_diff
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1085023003
2 files changed