Remove sql/ folder

[wgwz]

This should have been removed as part of #45. It's just a folder that we were storing old migrations in. These are no longer needed.

[paul121]

Note: this sql folder and old migrations are currently used in other places. Before removing here, these other places should be updated to the current graphile-migrate approach for migrations.

I'm still familiarizing myself but noticed sql/run_all_migrations.sh is at least being used in the Docker setup for regen-web: https://github.com/regen-network/regen-web/blob/8789af04941afed2ed582912ff082d7c8ffb9512/docker/scripts/indexer_init.sh#L3-L5

[wgwz]

IIRC I think that is only place we're using it. FWIW - the indexer is pinned to a particular commit with regen-web though - https://github.com/regen-network/regen-web/blob/8789af04941afed2ed582912ff082d7c8ffb9512/docker/indexer.Dockerfile#L8C19-L8C59

Just to say that the regen-web setup wouldn't break immediately upon making this change.

[paul121]

Thanks @wgwz ! I just opened a PR to update this in regen-web: regen-network/regen-web#2268