XWIKI-10549: Drop-down lists from Administration -> Logging have a larger width after setting a value

- Having the same text for ÔDefaultÕÕs value and label, since there are differences between Chrome and FF browsers
- Removing size=Ô1Õ since this is the default and Bootstrap provides special styling for size>1

(cherry picked from commit e290b3f61826acb3d19fc3b78230997be92021f8)