Revert "[rust png] Reinforce `testonly`-ness of some users of `libpng`."

This reverts commit e800913378944238d93efb337e76afb44af08dfd.

Reason for revert: Causing some bots failure: https://ci.chromium.org/ui/p/chromium/builders/ci/Libfuzzer%20Upload%20iOS%20Catalyst%20Debug/116009/overview
Or https://ci.chromium.org/ui/p/chromium/builders/ci/ios-catalyst/201046/overview

Original change's description:
> [rust png] Reinforce `testonly`-ness of some users of `libpng`.
>
> This CL extracts a separate `third_party/libpng:libpng_for_testonly`
> target which:
>
> 1) Is a `group` that proxies/forwards to the `libpng` target by listing
>    it as its `public_deps`
> 2) Has limited visibility (based on the new `libpng_testonly_visibility`
>    introduced in the refactored `third_party/libpng/visibility.gni`).
>    The new visibility is almost unchanged, except for explicitly
>    spelling out some targets instead of using wildcards
> 3) Is marked as `testonly`
>
> Bug: 443128323
> Change-Id: I15626f7ece79304f9649057e7e215c3e72d15b92
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6976870
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Commit-Queue: Ɓukasz Anforowicz <lukasza@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1521521}

Bug: 443128323
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I106b084528894950a44f52ce7e84c002c54a007e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6990712
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Yi Gu <yigu@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1521554}
NOKEYCHECK=True
GitOrigin-RevId: 7fa4c2d7ab42a48247ce8e0290cbb7e854990f1e
diff --git a/BUILD.gn b/BUILD.gn
index 3e31348..d4bdea1 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -130,14 +130,6 @@
   }
 }
 
-group("libpng_for_testonly") {
-  testonly = true
-  public_deps = [ ":libpng" ]
-
-  visibility = []
-  visibility = libpng_testonly_visibility
-}
-
 if (build_with_chromium) {
   libpng_ossfuzz_seed_corpuses = [
     "//components/test/data/viz",
diff --git a/visibility.gni b/visibility.gni
index a53ccd5..e7a8dc8 100644
--- a/visibility.gni
+++ b/visibility.gni
@@ -1,62 +1,23 @@
 # This list tracks all current users of libpng.
 # libpng is actively being migrated, and calls to libpng should instead go
-# through Skia's `SkPngRustDecoder`. No new entries should be added to this
-# list.
-
-# Chrome => ... => libpng dependencies.
-#
-# TODO(https://crbug.com/443128323): Stop exposing `libpng` to Chrome
-# (i.e. we should work on removing all entries on the list below).
+# through skia. No new entries should be added to this list.
 visibility = [
-  # Chrome => Skia => libpng dependency.
-  #
-  # TODO(https://crbug.com/381900683): Remove once Skia supports being
-  # built without `libpng`.
+  "//chrome/test:*",
   "//skia/*",
-
-  # Chrome => ... => freetype => libpng dependency.
-  #
-  # TODO(https://crbug.com/42271123): Remove this once `freetype` has been
-  # replaced with Fontations in PDFium and in other Chrome dependencies.
+  "//testing/libfuzzer/fuzzers/*",
+  "//third_party/angle/src/tests/*",
+  "//third_party/angle/third_party/glmark2:*",
+  "//third_party/angle/util:*",
   "//third_party/freetype:*",
-
-  # Chrome => PDFium => libpng dependency.
-  #
-  # TODO(https://crbug.com/444045690): Remove once PDFium => `libpng`
-  # dependency has been made optional.
-  "//third_party:png",  # In standalone PDFium
-  "//third_party/pdfium/third_party:png",  # In Chromium
-
-  # Other dependency edges that seem like Chrome => ... => libpng dependencies
-  # but really aren't.  TODO: Clarify this comment in follow-up CLs.
+  "//third_party/libpng/*",
   "//third_party/libwebp:*",
   "//third_party/weston/*",
-]
-
-# Test/tool-only dependencies under `//third_party/angle`
-# (migrating these to `libpng_testonly_visibility` would require editing
-# ANGLE's `BUILD.gn` files to depend on the `libpng_for_testonly` target).
-visibility += [
-  "//third_party/angle/src/tests:angle_deqp_framework_qphelper",
-  "//third_party/angle/third_party/glmark2:glmark2_common_gl",
-  "//third_party/angle/third_party/glmark2:glmark2_common_gles",
-  "//third_party/angle/util:angle_png_utils",
-]
-
-# Test/tool-only dependencies.
-libpng_testonly_visibility = [
-  "//chrome/test:accessibility_live_site_tests",
-  "//chrome/test:captured_sites_interactive_tests",
-  "//chrome/test:interactive_ui_tests",
-  "//testing/libfuzzer/fuzzers:libpng_progressive_read_fuzzer",
-  "//tools/imagediff",
-
-  # Using a wildcard, to cover template-generated targets (e.g.
-  # `//ui/gfx:gfx_unittests__library__jni_registration__native_sources` or
-  # `//ui/gfx:gfx_unittests__exec`).
+  "//tools/imagediff:*",
   "//ui/gfx:*",
 ]
 
-# Self-dependency (for internal targets defined in
-# `//third_party/libpng/BUILD.gn`).
-visibility += [ "//third_party/libpng/*" ]
+# PDFium dependency.
+visibility += [
+  "//third_party:png",  # In standalone PDFium
+  "//third_party/pdfium/third_party:png",  # In Chromium
+]