Remove CSS regions support, keeping a bare minimum to support "region-based" multicol.

Source/core/css/CSSRule.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * (C) 2002-2003 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2002, 2006, 2007, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Andreas Kling (kling@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 35 matching lines @@
         PAGE_RULE,
         // 7 was VARIABLES_RULE; we now match other browsers with 7 as
         // KEYFRAMES_RULE:
         // <https://bugs.webkit.org/show_bug.cgi?id=71293>.
         KEYFRAMES_RULE,
         WEBKIT_KEYFRAMES_RULE = KEYFRAMES_RULE,
         KEYFRAME_RULE,
         WEBKIT_KEYFRAME_RULE = KEYFRAME_RULE,
         SUPPORTS_RULE = 12,
         VIEWPORT_RULE = 15,
-        WEBKIT_REGION_RULE = 16,
         WEBKIT_FILTER_RULE = 17
     };
 
     virtual Type type() const = 0;
     virtual String cssText() const = 0;
     virtual void reattach(StyleRuleBase*) = 0;
 
     void setParentStyleSheet(CSSStyleSheet* styleSheet)
     {
         m_parentIsRule = false;
@@ skipping 40 matching lines @@
         CSSStyleSheet* m_parentStyleSheet;
     };
 };
 
 #define DEFINE_CSS_RULE_TYPE_CASTS(ToType, TYPE_NAME) \
     DEFINE_TYPE_CASTS(ToType, CSSRule, rule, rule->type() == CSSRule::TYPE_NAME, rule.type() == CSSRule::TYPE_NAME)
 
 } // namespace WebCore
 
 #endif // CSSRule_h