Remove field set label on reference edit dialog

Objective:

* Allow fieldsets to not have labels
* Remove label from reference edit dialog field set

Changes:

ve.ui.Layout.css
* Only apply negative top margin if fieldset label is being used

ve.ui.FieldsetLayout.js
* Only add label element to DOM if icon or label are used

ve.ui.MWReferenceEditDialog.js
* Remove label from reference edit dialog's first fieldset

*.php
* Remove unused message

Change-Id: I4a36e819ec6ef73aad80d3fb2f06000cb35ec109
Merge "Remove field set label on reference edit dialog"