org-contacts.el: Use `bound-and-true-p' to check (unbound) var

* org-contacts.el (org-contacts-link-store): Use `bound-and-true-p' to
check the truthiness of org-id-link-to-org-use-id, which may or may
not be bound depending on whether org-id has been loaded.  This
simplifies the code.

contrib/lisp/org-contacts.el

@@ -1166,7 +1166,7 @@ are effectively trimmed).  If nil, all zero-length substrings are retained."
   "Store the contact in `org-contacts-files' with a link."
   (when (and (eq major-mode 'org-mode)
 	     (member (buffer-file-name) (mapcar 'expand-file-name org-contacts-files)))
-    (if (and (featurep 'org-id) org-id-link-to-org-use-id)
+    (if (bound-and-true-p org-id-link-to-org-use-id)
 	(org-id-store-link)
       (let ((headline-str (substring-no-properties (org-get-heading t t t t))))
 	(org-store-link-props