🥀 rip skip_demo

Thanks to @KSK for converting the “stack demo” into an eups product and allowing DM-7556 to be cleanly implemented. The demo now runs as part of the build of the lsst_ci product. The SKIP_DEMO button has removed from the stack-os-matrix (and related) jobs and lsst_ci is now part of the default product list. The expectation is that lsst_ci will be ‘built’ prior to a merge to master.