[BUGFIX] Adjust css in new content element wizard

The rendering of the plugin menu gets messed up if a plugin hasn't any
description. This patch clears floating for every list item to ensure
it is displayed on the left side.

Resolves: #53895
Releases: 6.2
Change-Id: Ib64b99865fda1359ade4b7c22d160fbfe28350c9
Reviewed-on: https://review.typo3.org/25655
Reviewed-by: Wouter Wolters
Reviewed-by: Marcin Sągol
Reviewed-by: Stefan Froemken
Tested-by: Stefan Froemken
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter