Ensure all endpoints necessary for linux disk encryption do not throw "MDM is not enabled" error

[jacobshandling]

Follow-up to Allow disk encryption, summary APIs even when MDM not enabled, per this slack discussion.

Double-check if endpoint is being used for Linux disk encryption. If it is, remove MDM-enabled checking from it, and update relevant tests. See this slice.

1) Related to bug discussed in Slack:

• [ ] "GET", "/api/latest/fleet/mdm/hosts/1/encryption_key"
• [ ] "GET", "/api/latest/fleet/hosts/1/encryption_key"

2) Others:

• [ ] "GET", "/api/latest/fleet/mdm/profiles/summary"
• [ ] "GET", "/api/latest/fleet/disk_encryption"

[fleet-release]

Linux disk shields gleam, MDM not a dream. Fleet soars, unchained, serene.