[TASK] Remove COMPOSER_ROOT_VERSION from bamboo testing

With latest changes in master and helper repositories, we do
not need the COMPOSER_ROOT_VERSION setting in tests anymore.
Remove that to have one detail less to maintain.

Resolves: #87170
Releases: master
Change-Id: Iea54bb6f17d0b08b4b248c40ad60691aa5cb0cb3
Reviewed-on: https://review.typo3.org/59165


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>