Migration to mg_amc 2.2.1 and lhapdf6 (and remove old scripts)

With this the new scripts support all needed functionality for initial production (both LO and NLO) and are nominally production ready.  (Or will be once corresponding CMSSW 53x and 71x releases are available)

Removing old scripts as well to avoid confusion (they can still be accessed from the "legacy" tag: https://github.com/cms-sw/genproductions/tree/legacyMadgraph/bin/MadGraph)