Legacy runner: remove avocado.Test.*runner_queue*

[clebergnu]

Is your feature request related to a problem? Please describe. The runner_queue property of avocado.Test (and related methods and attributes) is used by the legacy runner only. It can and should be removed.

Describe the solution you'd like The complete removal of this "internal machinery" properties, methods and attributes.

Describe alternatives you've considered None.

Additional information While the interface of avocado.Test needs to be kept stable and have a deprecation period, I understand that this interface is highly private in purpose (while unfortunately being public in Python's OO sense). Also, the legacy runner has already being deprecated and is being dismantled.

For those reasons, IMO it can be removed without a deprecation period.

This is part of https://github.com/avocado-framework/avocado/issues/5138