Delete unnecessary/irrelevant files.

`cruise.aliases` contains some very specific aliases that could be helpful in some cases but would probably better fit in the doc.
`capfile` and `perf.capfile` contain thoughtworks' infrastructure specific data and hence are probably useless for the open-source version of Go.

(Fixes https://github.com/gocd/gocd/issues/261 and https://github.com/gocd/gocd/issues/260)