Bug(ontap-nas-qtree): unused FlexVols not cleaned up

[clementnuss]

Describe the bug
The code calling the pruneUnusedFlexVols function has been commented 5 years ago in this commit by @clintonk.

As a result, unused flexVols never get cleaned up 🤦🏼

Environment
Provide accurate information about the environment to help us reproduce the issue.

• Trident version: 24.06, but any version starting from 19.xx mostly

To Reproduce
Steps to reproduce the behavior:

Create a few flexVol with the ontap-nas-economy (ontap-nas-qtree in the code) and observe that FlexVols never get cleaned up.

Expected behavior
The code should be uncommented, the housekeeping task should run, and unused FlexVols should be cleaned up.

@clintonk can you remember the rationale ?

As an enterprise user of netapp, we have to spend time chasing around deleted_ Qtrees and empty FlexVols. The feature should at least be made optional in my eyes