Since gridtree bases on vaadin components the iframe issue is no issue any
longer, so we can roollback this hacky solution.

Revert "Use clientHeight for small iframes."

This reverts commit 03aefd77d67b07886bf96b12f373145cdcc54c69.
Cleanup VAutoHeightIFrame.
Merge remote-tracking branch 'korpling/annis/develop' into develop