Revert of Bring back compiling third_party/libpng in public.bzl (patchset #3 id:40001 of https://codereview.chromium.org/2044703006/ )

Reason for revert:
Breaking Google3

Original issue's description:
> Bring back compiling third_party/libpng in public.bzl
>
> Disable the optimizations for simplicity, as suggested in [1].
>
> Remove PNG_SKIP_SETJMP_CHECK, which is not defined in version 1.6.22.
>
> [1] https://codereview.chromium.org/2033063003/diff/20001/public.bzl#newcode84
>
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2044703006
>
> Committed: https://skia.googlesource.com/skia/+/e6939c15dc0c09f1348988dc56e50b6bea27b7ce

TBR=benjaminwagner@google.com,msarett@google.com,mtklein@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2090643002
diff --git a/public.bzl b/public.bzl
index 5ba5612..f84abc0 100644
--- a/public.bzl
+++ b/public.bzl
@@ -79,9 +79,6 @@
         "third_party/etc1/*.h",
         "third_party/ktx/*.cpp",
         "third_party/ktx/*.h",
-
-        "third_party/libpng/*.c",
-        "third_party/libpng/*.h",
     ],
     exclude = PRIVATE_HDRS_LIST + [
         # Exclude platform-dependent files.
@@ -386,7 +383,6 @@
     "src/utils",
     "third_party/etc1",
     "third_party/ktx",
-    "third_party/libpng",
 ]
 
 ################################################################################
@@ -551,17 +547,15 @@
 ################################################################################
 
 DEFINES_UNIX = [
+    "PNG_SKIP_SETJMP_CHECK",
     "SK_BUILD_FOR_UNIX",
     "SK_SAMPLES_FOR_X",
     "SK_SFNTLY_SUBSETTER",
     "SK_CODEC_DECODES_RAW",
     "SK_HAS_GIF_LIBRARY",
     "SK_HAS_JPEG_LIBRARY",
-    "SK_HAS_WEBP_LIBRARY",
     "SK_HAS_PNG_LIBRARY",
-    "PNG_ARM_NEON_OPT=0",
-    "PNG_INTEL_SSE_OPT=0",
-    "PNG_ARM_NEON_IMPLEMENTATION=0",
+    "SK_HAS_WEBP_LIBRARY",
 ]
 
 DEFINES_ANDROID = [
@@ -569,11 +563,8 @@
     "SK_CODEC_DECODES_RAW",
     "SK_HAS_GIF_LIBRARY",
     "SK_HAS_JPEG_LIBRARY",
-    "SK_HAS_WEBP_LIBRARY",
     "SK_HAS_PNG_LIBRARY",
-    "PNG_ARM_NEON_OPT=0",
-    "PNG_INTEL_SSE_OPT=0",
-    "PNG_ARM_NEON_IMPLEMENTATION=0",
+    "SK_HAS_WEBP_LIBRARY",
 ]
 
 DEFINES_IOS = [