Fix :after keyword

Commit [1] broke the functionality of :after (see [2]) due to an
extraneous quote being added.

[1]: bd2afa53c7
[2]: https://github.com/jwiegley/use-package/pull/433#issuecomment-287606553

lisp/use-package/use-package.el

@@ -1270,7 +1270,7 @@ deferred until the prefix key sequence is pressed."
                        `(,@(when (eq (plist-get state :defer-install) :ensure)
                              `((use-package-install-deferred-package
                                 'name :after)))
-                         '(require (quote ,name) nil t))))))
+                         (require (quote ,name) nil t))))))
      body)))
 
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