remove default stream of c9s mariadb
A mariadb module stream has been marked as default by accident in c9s.
From the commit message "ENGCMP-3649: Add default profile for module mariadb:10.11" I believe they only wanted to set a default profile, not a default stream.
This should unset the default stream, while keeping the default profile.
Fixes: RHEL-25802 and OSCI-6392 and https://lists.centos.org/pipermail/centos-devel/2024-February/165547.html