Use `delq nil' instead of `delete nil' in a few functions

* org.el (org-store-link): Use `delq nil' instead of `delete nil'.

* org-pcomplete.el (pcomplete/org-mode/drawer): Ditto.

* org-mobile.el (org-mobile-files-alist): Ditto.

lisp/org-mobile.el

@@ -276,7 +276,7 @@ Also exclude files matching `org-mobile-files-exclude-regexp'."
 		      (list f))
 		     (t nil)))
 		  org-mobile-files)))
-	 (files (delete
+	 (files (delq
 		 nil
 		 (mapcar (lambda (f)
 			   (unless (and (not (string= org-mobile-files-exclude-regexp ""))

lisp/org-pcomplete.el

@@ -290,7 +290,7 @@ This needs more work, to handle headings with lots of spaces in them."
 	(cpllist (mapcar (lambda (x) (concat x ": ")) org-drawers)))
     (pcomplete-here cpllist
 		    (substring pcomplete-stub 1)
-		    (unless (or (not (delete
+		    (unless (or (not (delq
 				      nil
 				      (mapcar (lambda(x)
 						(string-match (substring pcomplete-stub 1) x))

lisp/org.el

@@ -8898,7 +8898,7 @@ part of Org's core."
      (cond
       ((and (not (equal arg '(16)))
 	    (setq sfuns
-		  (delete
+		  (delq
 		   nil (mapcar (lambda (f) (let (fs) (if (funcall f) (push f fs))))
 			       org-store-link-functions))
 		  sfunsn (mapcar (lambda (fu) (symbol-name (car fu))) sfuns))