Disjoin current ns from candidate namespaces

If a user moves `myvar` from `my.ns.a` to `my.longer.ns.b` then runs
slamhound on `my.ns.a` to refer the var from `my.longer.ns.b`m slamhound
constructs the following ns:

(ns my.ns.a
  (:require [my.ns.a :refer [myvar]]))

This throws a circular dependency error and should be avoided.