Remove disabled/old bigcouch neighbors

root@manatee:~#     curl --netrc-file /etc/couchdb/couchdb.netrc -X GET 'http://127.0.0.1:5986/nodes/_all_docs'
{"total_rows":4,"offset":0,"rows":[
{"id":"bigcouch@giraffe.bitmask.net","key":"bigcouch@giraffe.bitmask.net","value":{"rev":"1-967a00dff5e02add41819138abb3284d"}},
{"id":"bigcouch@manatee.bitmask.net","key":"bigcouch@manatee.bitmask.net","value":{"rev":"1-967a00dff5e02add41819138abb3284d"}},
{"id":"bigcouch@snake.bitmask.net","key":"bigcouch@snake.bitmask.net","value":{"rev":"1-967a00dff5e02add41819138abb3284d"}},
{"id":"bigcouch@worm.bitmask.net","key":"bigcouch@worm.bitmask.net","value":{"rev":"1-967a00dff5e02add41819138abb3284d"}}
]}

sanke + giraffe are disabled, but still registered as neighbors on manatee

(from redmine: created on 2013-07-01, relates #2658 (closed))