DAL/Store: fix #4457

What

Stacked on !13216 (merged).

Fix #4457 (closed).

Why

How

Now that there is only one family of path remaining in the Irmin legacy store, we define it as an explicit list instead of snocing suffixes one by one.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
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