The `define-lambda-to-define` rule ought to be split

[jackfirth]

The define-lambda-to-define rule works on both ordinary (define id (lambda ...)) forms and also (define (func ...) (lambda ...)) forms. But the rule description is written assuming it's for the (define id (lambda ...)) form. Covering these two cases with separate rules and separate messages would make this refactoring a little more readable.