Remove CSS.unregisterProperty as the WG resolved to remove it for now

third_party/WebKit/Source/core/css/PropertyRegistry.cpp

Index: third_party/WebKit/Source/core/css/PropertyRegistry.cpp
diff --git a/third_party/WebKit/Source/core/css/PropertyRegistry.cpp b/third_party/WebKit/Source/core/css/PropertyRegistry.cpp
index 9a16144b41d22f95fc2692a4a976f999b72a8d42..fb0229591a5069f5e2916396aa1767fb695c0466 100644
--- a/third_party/WebKit/Source/core/css/PropertyRegistry.cpp
+++ b/third_party/WebKit/Source/core/css/PropertyRegistry.cpp
@@ -17,11 +17,6 @@ void PropertyRegistry::registerProperty(
       name, new Registration(syntax, inherits, initial, initialVariableData));
 }
 
-void PropertyRegistry::unregisterProperty(const AtomicString& name) {
-  DCHECK(registration(name));
-  m_registrations.remove(name);
-}
-
 const PropertyRegistry::Registration* PropertyRegistry::registration(
     const AtomicString& name) const {
   return m_registrations.get(name);