v1.55.0

Remove `check` command (#364)

This is now superseded by the ehrQL permissions system:
 * https://github.com/opensafely-core/ehrql/pull/2543

Note that this PR should not be merged until the related
`research-action` PR has been merged, which removes the one usage of the
`opensafely check` command:
 * https://github.com/opensafely-core/research-action/pull/115

Note that we deliberately leave the `repository_permissions.yaml` file
in place to avoid triggering errors on clients which haven't yet updated
and are still trying to fetch this file. I've set a reminder to remove
this file in a couple of weeks.