Remove old presentations from phenopackets.org splash page

[cmungall]

http://phenopackets.org/

It looks like someone recently removed a lot of the old stale text from the page, thanks!

There are still links to very out of date presentations:

Processing phenotype data using Phenopackets-API and PXFTools
BOSC 2016 Slides Video
Phenopackets: Making phenotype profiles FAIR++ for disease diagnosis and discovery
Force2016 Slides

I would remove these. Perhaps have some history section tucked away in the github repo docs.

Also there is a non-link phenopackets_org_email_placeholder

[pnrobinson]

@cmungall We are updating the documentation at the GA4GH website and I am going through the issues. I think we did a tiny update to the above page, but never really made much out of it. If you would like I can make a few modest changes to http://phenopackets.org/ to bring it up to date, but I would need to be made admin. I would suggest that we use this page to make a list of software products etc that use the schema.