DAL: upgrade store from v20

What

Upgrade it from octez release v20.

Why

Because octez release v20's store is not compatible with the current version.

How

The following is done:

• removed known (to me) Irmin files and directories; is there a better approach?
• removed the shard_store directory
• renamed skip_list to skip_lit_store (note: Lwt_unix.rename does not work on non-empty directories)

NOTE: profiles.json is not handed in this MR, it will be handled separately.

Manually testing the MR

Take the store of a v20 DAL node and start a DAL node on it using this branch.