(PDB-240) Replace anonymize.clj read-string with clojure.edn/read-string

This patch replaces a call to read-string in anonymize.clj with a call to
clojure.edn/read-string. Unlike clojure.core/read-string,
clojure.edn/read-string is safe to use with untrusted data and guaranteed to
be free of side-effects.
Merge pull request #996 from wkalt/ticket/master/pdb-240-swap-anonymize-read-string

(PDB-240) Replace anonymize.clj read-string with clojure.edn/read-string