[TASK] Deprecated Big/Small/Medium/Standard-Document

Deprecates classes:

- BigDocumentTemplate
- SmallDocumentTemplate
- MediumDocumentTemplate
- StandardDocumentTemplate

These classes are rarely used.
Also the standard style in the backend move along.

Resolves: #45955
Releases: 6.1
Change-Id: Ic6e261eef960a71f56a8c5af4724f24e5da8e32c
Reviewed-on: https://review.typo3.org/18555
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Magdalena Leichsenring
Tested-by: Magdalena Leichsenring