[BUGFIX] Do not show dropdown arrow if maxItems=1

A new CSS class is introduced to disable the dropdown arrow for select
boxes if a select box can only contain one item.

Resolves: #77665
Releases: master, 7.6
Change-Id: I095070e833a02728c9d2edd91a33919c0fbaf749
Reviewed-on: https://review.typo3.org/49708


Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Frans Saris <franssaris@gmail.com>
Tested-by: Frans Saris <franssaris@gmail.com>