HTCONDOR-1265: Use singularity from the OS
HTCONDOR-1265: Use singularity from the OS

The PATh-Facility pilot runs in a container whose image we own, and so
singularity should already be configured correctly.

htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor