Only validate that incremental streams have state before migrating connection to per-stream

[evantahler]

We have a check (#14599 / #14519) when migrating syncs to per-stream state that ensures that every enabled stream has state before migrating. However, this check should only happen for incremental streams

[lmossman]

I don't think this ticket is necessary. The validation only checks if the state that was produced at the end of the sync has states for all streams in the catalog, before it writes that state to the database. So this shouldn't matter if a sync had ran before or not

[evantahler]

Title & description updated