`define-typed-syntax` should error if rule has neither <= input or => conclusion

With this lang:
```racket
;; file no-arrow-lang.rkt
#lang turnstile/quicklang
(provide void Int)
(define-base-type Int)
(define-typed-syntax (void) ≫ 
  --------
 [⊢ (void-)])
```

this program produces no errors:
```racket
#lang s-exp "no-arrow-lang.rkt"
(require turnstile/rackunit-typechecking)
(check-type (void) : Int)
```
