rsc: Optimize blob eviction deletion

[V-FEXrt]

• Adds index to blob(updated_at) which speeds up the TTL check for old blobs
• Completes the blob eviction lookup and delete in one query to not waste time repeating work.
• Makes delete query much more static instead of passing in 16k variables

[V-FEXrt]

I imagine we used to do something else with the blobs between the fetch and the deletion?

Not really. It was previously just split into two queries for simplicity reasons