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

Source/core/rendering/RegionOversetState.h

-/*
- * 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.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Library General Public License for more details.
- *
- * You should have received a copy of the GNU Library General Public License
- * along with this library; see the file COPYING.LIB.  If not, write to
- * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
- * Boston, MA 02110-1301, USA.
- *
- */
-
-#ifndef RegionOversetState_h
-#define RegionOversetState_h
-
-namespace WebCore {
-
-enum RegionOversetState {
-    RegionUndefined,
-    RegionEmpty,
-    RegionFit,
-    RegionOverset
-};
-
-} // namespace WebCore
-
-#endif // RegionOversetState_h