Remove old presentations from phenopackets.org splash page

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There are still links to very out of date presentations: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 ](https://www.open-bio.org/wiki/BOSC_2016) [Slides ](https://f1000research.com/slides/5-1649) [Video](https://www.youtube.com/watch?v=8UreKE1eGNY)
Phenopackets: Making phenotype profiles FAIR++ for disease diagnosis and discovery
[Force2016 ](https://www.force11.org/meetings/force2016) [Slides](https://figshare.com/articles/Phenopackets_Making_phenotype_profiles_FAIR_for_disease_diagnosis_and_discovery/3180898)

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](mailto:phenopackets_org_email_placeholder)

Start at the phenopackets.org splash page and locate its source in the phenopacket-schema repository, using the repository docs as the likely place to check. The work is done when the two listed presentations and the phenopackets_org_email_placeholder link are removed, with any retained history handled as described in the issue.

Written by the indexing model from the issue text.