refactor tearDownRing to be used standalone

Background

This feature is added as a part of a study task for Dahyeon. https://jira.ess.eu/browse/ICSHWI-20634

Feature

Implement tearDownOneRing functionality, that tears down one ring instead of all rings.

Adjacent issues found

• call to setDomXcvr is discovered to be unnecessary in tearDownAllRings().