Remove `del` from `DataModel`. #1526

Job	Run time
test_upstream / Load tox environments	9s
test / Load tox environments	7s
test_upstream / rad (ubuntu-latest)	1m 45s
test / py39-oldestdeps-cov (ubuntu-latest)	3m 3s
test / py39 (ubuntu-latest)	1m 48s
test / py310 (ubuntu-latest)	2m 17s
test / py311 (ubuntu-latest)	2m 17s
test / py311 (macos-latest)	3m 15s
test / py311-cov (ubuntu-latest)	2m 11s
	16m 52s

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