Fix flakiness in fast/multicol/shrink-to-column-height-for-pagination.html.

setTimeout here is totally unnecessary.

Review URL: https://codereview.chromium.org/151843009

git-svn-id: svn://svn.chromium.org/blink/trunk@166550 bbb929c8-8fbe-4397-9dbb-9b2b20218538