Fix 2 occurrences of format-identity

This use of `format` does nothing.

Author: resyntax-ci[bot]

typed-racket-lib/typed-racket/typecheck/error-message.rkt

@@ -80,9 +80,9 @@
   (unless object?
     (when (and (F? row) (not (F? row*)))
       (type-mismatch (format "Class with row variable `~a'" row)
-                     (format "Class with no row variable")))
+                     "Class with no row variable"))
     (when (and (F? row*) (not (F? row)))
-      (type-mismatch (format "Class with no row variable")
+      (type-mismatch "Class with no row variable"
                      (format "Class with row variable `~a'" row*)))
     (when (and (F? row) (F? row) (not (equal? row row*)))
       (type-mismatch (format "Class with row variable `~a'" row)