Drop SQLite migration support
We should remove all support for running migrations on/from SQLite. This significantly cleans up the migration environment.
- Almost 50% of the code in the migration environment consists of legacy SQLite backups code. This code will never be used again.
- The initial migration reads data from SQLite using the current db metadata. Will never be used again, and will break in the future if we ever add new tables.
Edited by Hugo Kerstens