Remove deprecated v13 tbot config migration

[strideynet]

Teleport V14 shipped with a new configuration format for Machine ID, we migrated on-the-fly from V13 to the new format, and provided tooling to persist this migration. This PR removes support for this migration starting from V17.

changelog: BREAKING: The tbot binary no longer supports the V1 configuration format that was deprecated from V14. See https://goteleport.com/docs/machine-id/reference/v17-upgrade-guide/ for more information.

[zmb3]

Do we have any idea how prevalent the deprecated format is in the wild? CI/CD tends to be set and forget, so I wouldn't be surprised if this change catches people by surprise and breaks things.

[strideynet]

Do we have any idea how prevalent the deprecated format is in the wild? CI/CD tends to be set and forget, so I wouldn't be surprised if this change catches people by surprise and breaks things.

@zmb3 - we don't have analytics for this - but at least in my experience, it's been at least 3 months since I've seen this in the wild. I can take a slightly less aggressive approach if you'd prefer whereby in V17, we emit a fatal error that can be ignored with an environment variable and then in v18, we finally drop this code.

I do personally feel though that if we're talking about CI/CD in particular here, there's going to be some active step on behalf of the administrator to bump the major version - if they've chosen to ignore two breaking change warnings in major release notes and a warning message on start for three versions, then their first CI run after upgrading will result in a failure, and they can roll back to V16, run the migration, and then proceed to V17. I can modify the error log here to be a little more descriptive in the steps they need to take.

[timothyb89]

Not sure when we'll want to pull the trigger on this, but it looks good to me.

[zmb3]

@strideynet should we merge this for v18?