Simplify watched selector handling and remove remnants of user stylesheets

Source/core/css/RuntimeCSSEnabled.cpp

Index: Source/core/css/RuntimeCSSEnabled.cpp
diff --git a/Source/core/css/RuntimeCSSEnabled.cpp b/Source/core/css/RuntimeCSSEnabled.cpp
index 10699f69d81ec67a1d2a3881e05c8c4fdc3138d8..8aa5f6b989ea7f21f56337f498d52e0bdfa95596 100644
--- a/Source/core/css/RuntimeCSSEnabled.cpp
+++ b/Source/core/css/RuntimeCSSEnabled.cpp
@@ -103,9 +103,6 @@ static void setPropertySwitchesFromRuntimeFeatures()
     RuntimeCSSEnabled::setCSSPropertyEnabled(CSSPropertyColumnFill, RuntimeEnabledFeatures::regionBasedColumnsEnabled());
     RuntimeCSSEnabled::setCSSPropertyEnabled(CSSPropertyScrollBehavior, RuntimeEnabledFeatures::cssomSmoothScrollEnabled());
     RuntimeCSSEnabled::setCSSPropertyEnabled(CSSPropertyWillChange, RuntimeEnabledFeatures::cssWillChangeEnabled());
-
-    // InternalCallback is an implementation detail, rather than an experimental feature, and should never be exposed to the web.
-    RuntimeCSSEnabled::setCSSPropertyEnabled(CSSPropertyInternalCallback, false);
 }
 
 static CSSPropertySwitches& propertySwitches()