less: cleanup #quick_login style

- there are no #quick_login .links elements
- there are no #quick_login .buttons elements
- there are no #quick_login .form-group elements
- there are no #quick_login .unread elements
- there are no #quick_login .notifications elements
- color is already set on #quick_login *
- background and padding is already set for all dropdown menus
- h4 already has margin-bottom 10px