In the push to merge the large number of commits to agl-service-can-low-level in early 2020, we missed/forgot that part of the changes was dropping support of /etc/dev-mapping.conf.  This breaks user expectations and no longer matches the documentation, which was not changed.  Since manipulating the binding libappcontroller JSON to change the device mapping is not usefully documented and seems impractical with respect to the JSON file inside the installed widget, the previous behavior must be restored to fix setups like the AGL demo system (and soon the CI setup, which now has a requirement of specifying different devices).