Inspect usage of root-level PDF files (and delete if unused)

[jbum]

The PDFs in the root level don't look like they belong there (normally PDFs go into the pdfs/ directory).

• Check if any of these are being used by any active markup in the COVID19 directory. Redirect references if need be.
• Investigate how these were created and document here.
• Delete root-level PDFs.

[jbum]

I see most of these were added by Liz and Karim. A couple from Ashley.

I've confirmed that these don't exist in the cloud and are unused.

Checking with LIz if it's okay to remove them...

@LizNobriga says it's okay.

[jbum]

Relevant PR

#685