Remove stats

Right now also the stats are not working in Fauxton and we
decided to remove it right now.

In a serious production setup stats are provided by external
tools like collectd, graphite, monit and friends - we include
couchdb-folsom for that in 2.0.

Discussion on ML:
https://www.mail-archive.com/dev%40couchdb.apache.org/msg37245.html

Closes COUCHDB-2429

**Note**: 7d0aab0 is already on master but is not mirrored yet.