remove wgSpeedBox and related helper functions

wgSpeedBox was an old "hack" that rewrote the cache buster values based on last modified timestamp.  I think this was mostly an issue before we had the poz devboxes.  

As implemented it breaks when AllInOne=1, because the getSassFilePath() function fails to match against the asset paths because of the changed cb value.  Now that chrome dev tools can unminify the original js, the need for AllInOne is diminished, therefore the need for wgSpeedBox is diminished, and I'd like to remove it.  

@macbre