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

LayoutTests/fast/regions/script-tests/region-element-display-change.js

-description("Test that RenderObject is recreated correctly after changing display type.");
-
-function testElement(element, displayType)
-{
-        element.style.setProperty("display", displayType);
-        // The region element was created if the length of inner text is 0.
-    var regionCreated = element.innerText.length == 0;
-        return regionCreated;
-}
-
-var element = document.createElement("div");
-var textElement = document.createTextNode("inside element");
-element.appendChild(textElement);
-element.style.setProperty("-webkit-flow-from", "flow");
-document.body.appendChild(element);
-shouldBeFalse('testElement(element, "none")');
-shouldBeTrue('testElement(element, "block")');
-shouldBeTrue('testElement(element, "inline-block")');
-shouldBeFalse('testElement(element, "inline")');
-shouldBeFalse('testElement(element, "table")');
-shouldBeFalse('testElement(element, "inline-table")');
-shouldBeTrue('testElement(element, "table-cell")');
-shouldBeTrue('testElement(element, "table-caption")');
-shouldBeTrue('testElement(element, "list-item")');
-shouldBeFalse('testElement(element, "-webkit-box")');
-shouldBeFalse('testElement(element, "-webkit-inline-box")');
-shouldBeFalse('testElement(element, "-webkit-flex")');
-shouldBeFalse('testElement(element, "-webkit-inline-flex")');
-// FIXME: Also add grid and inline grid when it is enabled by default
-document.body.removeChild(element);