Disable buchets detection code, as we are not using it for now (bug 1003266)

https://bugzilla.mozilla.org/show_bug.cgi?id=1003266
I changed all the conditions to `!== undefined` since various jsperf tests showed that this was much faster across all browsers. It doesn't matter much if we end up deleting this in favor of the `has/getFeature` API, but I did it to test the performance difference (~ 30ms on my flame).