Update CONTRIBUTING.md
Update CONTRIBUTING.md

Removed links to non-publicly-accessible team links (though it seems strange that these aren't accesible).
opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core