[crdb] Remove useless indexes

[the-glu]

This PR contrib to general performance and to #813 by removing useless indexes in CRDB.

Cells index or primary keys should be used looking at queries, making those indexes useless.

ends_at / updated_at are not removed to use indexes when using evict tool.
owner on rid.subscriptions is used in MaxSubscriptionCountInCellsByOwner

Notice that not the case for yugabyte and nothing changed there.

[barroco]

@the-glu, thank you for this. Can you please provide evidence of no degradation ?

[the-glu]

@the-glu, thank you for this. Can you please provide evidence of no degradation ?

Performances tests I ran (locus ones) show no changes, but they are really synthetic.

This also really depends on the planner / statistics / data in the table, so it's mostly based on query analysis that measurable data.

[barroco]

Please update the NEXT_RELEASE_NOTES

[BenjaminPelletier]

This looks reasonable to me, but as @barroco notes, users with existing deployments will need/want to do something because of this change so we need something in NEXT_RELEASE_NOTES.

Beyond this PR, we should make sure it's clear how to perform a DB migration and what is and isn't required. Specifically, one user group thought they needed to synchronize the actions of all pool participants to a narrow time window to update both the schema and software version, while I think we have a design intent to avoid that need (instead allowing a leisurely schema update on the previous software version, then leisurely transitioning of each DSS instance to the new software version, or perhaps in the reverse order).

[the-glu]

Release notes updated