Revert "[CSS Regions] Mouse over an element does not trigger :hover state for parent when the element is flowed in a region"

This caused :hover on display: block elements to stop working.

This reverts commit e1ff7fe9066009c168694766822129ddccb9eac2.

BUG=253472
R=leviw@chromium.org

Review URL: https://codereview.chromium.org/19660002

git-svn-id: svn://svn.chromium.org/blink/trunk@154409 bbb929c8-8fbe-4397-9dbb-9b2b20218538