Refactor `Delete` workflow

**What would you like to be added**:
Refactor the `delete cluster` workflow to use the Management cluster field which was [added to the command context](https://github.com/aws/eks-anywhere/blob/3f6b8e36934306d4732ba0f9167bcaaa9c65e075/pkg/task/task.go#L35).

**Why is this needed**:
This change will be done to make naming consistent through out the workflows.

Start with pkg/task/task.go and the command context's Management cluster field linked in the issue, then trace the delete cluster command workflow. Done means the workflow uses that field and its naming is consistent with the other workflows; no tests are named, so identify the relevant validation while tracing it.

Written by the indexing model from the issue text.