Cleanup some more pagination dead code.

paginationUnit and behavesLikeColumns are both only ever set to
one value.

Review URL: https://codereview.chromium.org/148233010

git-svn-id: svn://svn.chromium.org/blink/trunk@166538 bbb929c8-8fbe-4397-9dbb-9b2b20218538