enable no unused using linter rule in azure rule set

That linting rule is automatically enabled in the IDE but we probably want that to be in spec repo too

The issue does not name a file or test. Locate the spec repository's Azure lint rule-set configuration, inspect how existing rules are enabled, and identify the setting for the no-unused-using rule. Done means the rule is enabled in that rule set and the repository's lint checks pass.

Written by the indexing model from the issue text.