Revert "Add ol.BrowserFeature.HAS_FULLSCREEN constant"

This reverts commit 5a940c207a0fd81562b491e3f2e3bfdd974d3592.

Detection of full screeen support requires the document to have a body.
This is not the case if ol3 is loaded in the head.  Therefore, defer the
test for full screen support to when it is needed.
Merge pull request #1776 from twpayne/fix-full-screen-test

Don't check for full screen support at load time