Migrate delete_key -> delete, new function sig

Again, this matches what the other clients seem to do.  The node client uses
"remove" instead of "delete", but that's new and I think "delete" maps to the
operation better.
Allow passing in an unquoted ref value.

Basically, allows you to use "12345" instead of "\"12345\""

This is backwards-compatible with quoted refs people might have stored.