Sometimes its the simple things that bite you in the butt.
I went back and reviewed the Problems getting started with duplicati thread. I saw @kenkendk’s comments about mono at …support-in-Mono
Debian Jessie (8.0)
The default Mono version is 3.2.8, which can run Duplicati, but lacks the cert-sync tools. Uninstall any Mono packages and then use the Mono supplied Debian packages, which will give you the latest version of Mono and the ca-certificates-mono package which fixes SSL.
After removing mono 3.2.8 and installing mono from mono-project.com (5.4.0.201 at this time) Google Drive file delete works! Life is good.