package-build--write-pkg-file: Go back to using emacs-lisp-mode

`lisp-data-mode' was only added in Emacs 28.1.

Closes melpa/melpa#9193.

package-build.el

@@ -1019,8 +1019,7 @@ Use a sandbox if `package-build--use-sandbox' is non-nil."
 (defun package-build--write-pkg-file (rcp dir)
   (pcase-let (((eieio name version summary dependencies) rcp))
     (with-temp-file (expand-file-name (format "%s-pkg.el" name) dir)
-      (insert
-       ";; -*- mode: lisp-data; no-byte-compile: t; lexical-binding: nil -*-\n")
+      (insert ";; -*- no-byte-compile: t; lexical-binding: nil -*-\n")
       (insert (format "(define-package \"%s\" \"%s\"\n" name version))
       (insert (format "  \"%s.\"\n" summary))
       (if dependencies