collectd: remove old workarounds

> Use system Python; doesn't compile against 2.7
Since... 10.7? the system python *is* 2.7, so this isn't true anymore.

> -C enables the cache and resolves permissions errors
I added this because it fixed a build error for someone, but in
hindsight it was probably indicative of a different problem.
icu4c: change keg_only reason
icu4c: update 53.1 bottle.