remove dispatch on Keywords (made useless by check on js/String) in elem...

cljs has no type for Keywords (not yet), meaning protocols have to check for `keyword?` on `default` or `js/String`, @ibdknox choose to do the later in c7259c983510b888a849ae54f2061a9c0d0d87ec , making the Keyword extension useless (actually it always was). 

here is a gist that shows this: https://gist.github.com/4104635