Remove sled_resource_vmm records without a VMM record

[smklein]

Fixes #7896

[hawkw]

This seems right to me, after reading through the discussion between you and @gjcolombo on #7896.

I did wonder briefly if perhaps we would want to do this periodically in case any erroneous records were accidentally created somehow, but I don't really think it's worth the effort, given that the current schema code really shouldn't ever do that.

[smklein]

This seems right to me, after reading through the discussion between you and @gjcolombo on #7896.

I did wonder briefly if perhaps we would want to do this periodically in case any erroneous records were accidentally created somehow, but I don't really think it's worth the effort, given that the current schema code really shouldn't ever do that.

I considered making this a background task, but the idea of doing this deletion seems like "one more interaction" with this table that I'd rather not have (e.g., could it cause issues on creation? deletion? etc). By making it a schema change, it's one-time, it can be tracked, and it happens when the system is in a quiesced state (for now).