Stop trying to build files that are not there

public.bzl

Index: public.bzl
diff --git a/public.bzl b/public.bzl
index bca4b789a2ebeef64244e5151bf9e3ce9c4656c5..f84abc0e6c9abca39049585ac77661f1fadd3d2c 100644
--- a/public.bzl
+++ b/public.bzl
@@ -79,9 +79,6 @@ BASE_SRCS_ALL = struct(
         "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 @@ INCLUDES = [
     "src/utils",
     "third_party/etc1",
     "third_party/ktx",
-    "third_party/libpng",
 ]
 
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