[BUGFIX] Remove inline style for margin and calculation of it

The rootpages in the site configuration do not have intendation any
longer. The computation of the margin value and the unused inline
style are removed.

Resolves: #104066
Releases: main, 12.4
Change-Id: Ic75d7e10638b2ee3fb06f42add1a36c180f754e7
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84635


Tested-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>