The `non_concurrent_rules` role is unused

[michelemin]

When booting Plaid, one can specify --no-non-concurrent which controls whether the instance has the non_concurrent_rules role or not.

The code for setting this appears to be correct, but that role is never checked or used in the code.

TODO:

• Fix the code to use the role: an instance should run rules marked as non-concurrent only if it has that role.