Deprecate legacy content in 05-data-models

[colmsnowplow]

In this repo, the data modeling directory: https://github.com/snowplow/snowplow/tree/master/5-data-modeling contains some content that can probably just be considered deprecated by now.

Specifically, the deduplication queries only apply to Redshift, and pre-date deduplication features in the pipeline. Perhaps they should still exist but this repo no longer feels like the appropriate place.

I'm not sure what the reference-data and event-manifest-populator directories are for, but it's worth figuring out how useful/appropriate they are for this repo. :)