Update LabelDescriptionDuplicateDetector documentation

... and remove an unused parameter.

This patch is not important, obviously. I think it's better to merge
most other patches first. I will rebase this later.

Change-Id: If45845564cace68d83daae6d3d4f446aa86fadf6
Never modify fingerprint when validating

Change-Id: I550e81ddc2ae0c918e5f3e8d7fffb6098ccb4eec
Merge "Never modify fingerprint when validating"
Merge "Update LabelDescriptionDuplicateDetector documentation"