Config: remove deprecated disable-precheck

Context

Remove the disable-mempool-precheck flag and disable_precheck field of the prevalidator configuration, that had been deprecated in !8963 (merged).

Fixes #5767 (closed).

Manually testing the MR

CI

Also, running a node with --disable-mempool-precheck now fails.

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