Don't underline a elements with the mw-ui-button class:

This is in addition to an existing 'text-decoration: none' on the class
itself.  This is being kept for other elements (e.g. button), but is
not specific enough to beat a conflicting declaration in commonElements.css

Change-Id: I8ec7efd97abad0ca75dea9b1c28e1fb91323741f
Merge "Don't underline a elements with the mw-ui-button class:"