V6 Bug - [Nav] - remove pf-m-expandable from examples

[tlabaj]

Describe the problem

pf-m-expandable no longer exists in Nav style sheet. It should be removed form example code.

How do you reproduce the problem?
You can see the modifier in examples with expandable nav (https://pf6.patternfly.org/components/navigation/#expanded)

Expected behavior
A clear and concise description of the expected behavior.

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last 60 days. It will be closed in 30 days if no further activity occurs.

[mcoker]

closed by #6727