Remove unused NodeListIsRootedAtDocumentIfOwnerHasItemrefAttr NodeListRootType value

Remove unused NodeListIsRootedAtDocumentIfOwnerHasItemrefAttr NodeListRootType value
and make the m_rootType bitfield smaller as a result.

R=adamk@chromium.org, esprehn@chromium.org, adamk, esprehn

Review URL: https://codereview.chromium.org/180393002

git-svn-id: svn://svn.chromium.org/blink/trunk@167846 bbb929c8-8fbe-4397-9dbb-9b2b20218538