Tezt: clean legacy attestation name encoding related tests

What

The time to put the legacy attestation name endorsement to sleep has come. This MR is part of a set that target to remove the support for this old name.

This MR removes deprecated support of endorsement in the tezt tests.

Why

How

Remove all Tezt helper code related to legacy attestation name

Manually testing the MR

CI green

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