Simplify BTAG_TrkVKalVrtFitterCfg
Configs should not discard properties explicitly provided by the user. At the moment, this is only called in https://gitlab.cern.ch/atlas/athena/-/blob/main/InnerDetector/InDetConfig/python/InDetVKalVxInJetToolConfig.py#L32
where the Extrapolator
is not set anyway, so it won't make any difference.