*8961* Cleanup usageStats warnings

Fix ambiguous reference to "Usage statistics plugin is disabled." message as "openFileFailed".  Also, remove English locale keys incorrectly in da_DK, pt_PT, and zh_CN locale files.
Users will only see this message if they are not using the auto stage scheduled task. So, to make it even more useful, I think we can add that users can use the auto stage scheduled tasks to process those files or they should move them manually to the stage folder again.