[Tei-council] REGENERATING, NOT!

Re: Stylesheets meeting further info BTW, passing REGENERATING=1 to the Stylesheets/Test/Makefile tells the Makefile to not bother doing all those `diff` commands, but it does NOT actually regenerate the expected_results/. I.e., it just generates the output files (like test15.odd.rnc), but does not move them into expected_results/. One would have to do that by hand. (I think this was a purposeful change by Martin or someone just to avoid clobbering all the expected_results/.) Moreover, back on 2020-03-18 Martin commented out the diffs of test21.rnc, test30.rnc, and test30.dtd. I think we should probably put those back, yes, Martin?