Revert "Use functions as format-spec substitutions when supported"

This reverts commit 77e8aa6.

`format-spec' makes a temporary buffer current for internal purposes.
Sadly does not undo that, while evaluating the substitution functions.
Our substitution functions expect to be called in the buffer, which
was current before this function is called.

Author: tarsius

lisp/transient.el

@@ -4772,27 +4772,18 @@ as a button."
 %k is formatted using `transient-format-key'.
 %d is formatted using `transient-format-description'.
 %v is formatted using `transient-format-value'."
-  (static-if (>= emacs-major-version 29)
-      (format-spec (oref obj format)
-                   `((?k . ,(lambda () (transient-format-key obj)))
-                     (?d . ,(lambda () (transient-format-description obj)))
-                     (?v . ,(lambda () (transient-format-value obj)))))
-    (format-spec (oref obj format)
-                 `((?k . ,(transient-format-key obj))
-                   (?d . ,(transient-format-description obj))
-                   (?v . ,(transient-format-value obj))))))
+  (format-spec (oref obj format)
+               `((?k . ,(transient-format-key obj))
+                 (?d . ,(transient-format-description obj))
+                 (?v . ,(transient-format-value obj)))))
 
 (cl-defmethod transient-format ((obj transient-suffix))
   "Return a string generated using OBJ's `format'.
 %k is formatted using `transient-format-key'.
 %d is formatted using `transient-format-description'."
-  (static-if (>= emacs-major-version 29)
-      (format-spec (oref obj format)
-                   `((?k . ,(lambda () (transient-format-key obj)))
-                     (?d . ,(lambda () (transient-format-description obj)))))
-    (format-spec (oref obj format)
-                 `((?k . ,(transient-format-key obj))
-                   (?d . ,(transient-format-description obj))))))
+  (format-spec (oref obj format)
+               `((?k . ,(transient-format-key obj))
+                 (?d . ,(transient-format-description obj)))))
 
 (cl-defgeneric transient-format-key (obj)
   "Format OBJ's `key' for display and return the result.")