lessChrome: Remove unnecessary code. Bookmark toolbar is part of the gNavToolbox.

These part of codes are added to solve problem in #516. I guess, at that time, bookmark toolbar is not part of the gNavToolbox. So we had to take into account bookmark toolbar's height separately. But (I don't know from when) now bookmark toolbar is part of the gNavToolbox. Therefore, it causes problem if we take into account its height twice. Specifically, web content move up or down when toolbox (with bookmark bar) is appear or disappear. This patch solve this problem.