Remove changed_when hack on file permissions task

[mtlynch]

The file permissions task reports a change on repeated runs even though nothing should have actually changed:

https://github.com/mtlynch/ansible-role-tinypilot/blob/21514df253b1fa9e6e6d390ef907f5544b2135eb/tasks/main.yml#L65

As a hack, I've placed changed_when: false to pass idempotence tests, but we should figure out why it's reporting a change here.