proc: remove a needless use of r5js.Datum#getType.
parse: quote canonicalization is done in reader, so don't bother in parser.
parse: inline last remaining use of r5js.Datum#getType.
datum: remove r5js.Datum#getType.
datum+runtime: remove apparently unnecessary r5js.Datum#sameTypeAs.
datum: remove two unnecessary references to r5js.Datum.type_.