Remove status:experimental for blink ForcedColors feature

This is because this blink runtime feature doesn't work by itself.
It's controlled by the corresponding Chromium feature which needs to
be enabled to make the whole feature work.

We'll continue to use the virtual test suites to test the feature.

Bug: 1121839
Change-Id: I902cf87e8fba8e1123dd4a6f5e6fe8c7f821f524
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2378631Reviewed-by: Alison Maher <almaher@microsoft.com>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802350}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -843,7 +843,9 @@
     // For simulating Android's overlay fullscreen video in web tests on Linux.
     {
       name: "ForcedColors",
-      status: "experimental",
+      // No status because this blink runtime feature doesn't work by itself.
+      // It's controlled by the corresponding Chromium feature which needs to
+      // be enabled to make the whole feature work.
     },
     {
       name: "ForceDeferScriptIntervention",