The HibernateDataMigrationManager continues checking for data migrations on a deleted wiki

When deleting a subwiki, the HibernateDataMigrationManager still checks for migrations on the deleted subwiki, therefore triggering regularly exceptions in logs, at least until the next server restart.

This could cause a problem in environments where exceptions in logs can trigger alerts and cause useless interventions on the server in order to investigate those exceptions.

One example of an exception thrown : https://up1.xwikisas.com/#Xw2f0b2YXoEP_jXVsnFB7w