Remove Olivero from database dumps

Problem/Motivation

Olivero is enabled in the 11.3.0 filled database dump, we can't update core with missing theme. Since default_admin doesn't exist in 11.3.0 the safest option here is probably to change the 11.3.0 dumps to use stark. We can then open a separate issue fro 11.4.0 dumps to use default_admin.

If Claro is set in any database dumps, we should switch that to Stark too at the same time.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet