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

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PropertyRegistry_h
 #define PropertyRegistry_h
 
 #include "core/css/CSSSyntaxDescriptor.h"
 #include "core/css/CSSValue.h"
 #include "core/css/CSSVariableData.h"
@@ skipping 33 matching lines @@
     const bool m_inherits;
     const Member<const CSSValue> m_initial;
     const RefPtr<CSSVariableData> m_initialVariableData;
   };
 
   void registerProperty(const AtomicString&,
                         const CSSSyntaxDescriptor&,
                         bool inherits,
                         const CSSValue* initial,
                         PassRefPtr<CSSVariableData> initialVariableData);
-  void unregisterProperty(const AtomicString&);
   const Registration* registration(const AtomicString&) const;
 
   DEFINE_INLINE_TRACE() { visitor->trace(m_registrations); }
 
  private:
   HeapHashMap<AtomicString, Member<Registration>> m_registrations;
 };
 
 }  // namespace blink
 
 #endif  // PropertyRegistry_h