[TASK] Remove template.php

Deleted the former central template file "template.php".
Template.php was deprecated and is scheduled for removal.

All remaining references to template.php are updated.
Template.php had only be referenced within comments.

Change-Id: I07b499b45d9bc83adcc9ea4ff10eae7aaa18c7d4
Resolves: #48122
Releases: 6.2
Reviewed-on: https://review.typo3.org/20725
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters