[TASK] Cleanup CssStyledContentController

* Make use of the "use" statement for GeneralUtility
* Long lines are spread over more lines for readability

Change-Id: Iea4bbfec9e672828fda5ad2d19f2d2a76268fa99
Resolves: #46902
Releases: 6.1
Reviewed-on: https://review.typo3.org/19551
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn