Remove sygus print callback (#4727)

Remove sygus print callback (#4727)

This removes sygus print callbacks, since they are no longer necessary to support the sygus v1 parser.

This involved generalizing the scope of the datatype utility sygusToBuiltin. Now, printing "as sygus" simply is accomplished by doing sygusToBuiltin conversion and then calling the printer on the builtin term.

This is required for further work towards eliminating the Expr layer.

FYI @4tXJ7f