remove references to GitHub in KPIs and guide once community metadata page is implemented

[tomkralidis]

As discussed at TT-WISMD 2021-05-21, we need to ensure working area URLs (like those here in GitHub) are not referenced in the KPIs or Guide. Rather, we will implement a metadata page on the WMO community website to which the KPIs and Guide will provide linkages to.

[amilan17]

https://community.wmo.int/activity-areas/wis/wcmp

[amilan17]

The KPI currently has a link to pywcmp in GitHub. Therefore, I think we can close this issue, unless that is not accepted by INFCOM.