packaging: do not use `%py_provides` for Python 2 #223

Job	Run time
Ubuntu 20.04 (clang++)	1m 48s
Ubuntu 22.04 (clang++ with sanitizers)	3m 28s
Ubuntu 20.04 (g++)	1m 26s
Ubuntu 22.04 (g++ with sanitizers)	3m 42s
	10m 24s

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