AFT-706: Move to SF eigen for b-tagging systematic

We should probably move to more sensible defaults for susytools. The default tagger here doesn't even exist in newer derivations, so that needs to change. Also we shouldn't default to "Envelope" systematic variations for flavor tagging. Marking this as a draft to see if @fdibello, @bmoser, @vvecchio, @bdong, or @ligang have any comments.

This is the main counterpart to !69078 (closed) (which targets 21.0). I'm not sure if changing 21.2 now is worth it, but hopefully changing this in main is less controversial.