Revert "Set created Merge Requests to unassigned"

This reverts commit 682b468d.

After upgrading Gitlab to 15.5 this feature seems to be broken and causes MR not to be created. Since our workflow has changed and now the MR filtering is done using reviewer let's revert the use of unassign.

https://phabricator.apertis.org/T9237

Signed-off-by: Walter Lozano walter.lozano@collabora.com