Remove `del` from `DataModel`. #1532

Job	Run time
test / Load tox environments	6s
test_upstream / Load tox environments	9s
test / py39-oldestdeps-cov (ubuntu-latest)	3m 0s
test / py39 (ubuntu-latest)	1m 59s
test / py310 (ubuntu-latest)	2m 11s
test / py311 (ubuntu-latest)	1m 30s
test / py311 (macos-latest)	3m 24s
test / py311-cov (ubuntu-latest)	2m 26s
test_upstream / rad (ubuntu-latest)	2m 27s
	17m 12s

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