TBR: If no GitHost is defined, don't set the project revisions.
TBR: If no GitHost is defined, don't set the project revisions.

They will default to HEAD.

I'm going to remove the git host from the mirror manifests, so everything should work.

Change-Id: Id7e8be868d483dd7696acc65b9029f668b944a4b

vanadium/go.jiri,vanadium/go.jiri