Storage: remove unnecessary check with storage commands

This simple MR removes a check that was done while running the octez-node storage command. Indeed, checking that store.0.suffix is invalid as, with GC, this file may be gone. Additionally, if no store file is available (which is unlikely to be the case), the irmin command will fail anyway.

Manually testing the MR

Run the octez-node storage integrity-check command on a data-dir

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).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR