[BUGFIX] Extension Manager: Use JsonView directly

There are several problems due to the implementation of JsonView
that returns spaces around a JSON returned to the extension manager
that will update the latest extensions.

Resolves: #75214
Releases: master
Change-Id: Iee837da392f62cd1df72c03dca0a03bb763c5790
Reviewed-on: https://review.typo3.org/47343


Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>