Remove isActiveInsertionPoint check from recalcStyle

NodeRenderingTraversal::parent returns null for active insertion points
after r161137 which means parentRenderStyle() would be null too so
there's no reason to have this check.

Review URL: https://codereview.chromium.org/59143003

git-svn-id: svn://svn.chromium.org/blink/trunk@161330 bbb929c8-8fbe-4397-9dbb-9b2b20218538