CORE-6113 Fix error messages in some metadactyl endpoints.

Updated thrown exception maps to use ':error_code' keys that the commons trap function expects, instead of the old ':code' keys metadactyl used to handle.
Added 401 status response for ERR_NOT_AUTHORIZED errors in clojure-commons.error-codes.
Updated metadactyl.user/store-current-user to use clojure-commons.error-codes/trap and to remove the user's password from exceptions.
Removed obsolete functions from metadactyl.util.service.