Remove non-existent property #41

Job	Run time
doctests	1m 51s
test (ubuntu-latest, x64, 1.6)	1m 19s
test (ubuntu-latest, x64, nightly)	2m 49s
test (ubuntu-latest, x86, 1.6)	2m 28s
test (ubuntu-latest, x86, nightly)	4m 47s
test (macOS-latest, x64, 1.6)	2m 20s
test (macOS-latest, x64, nightly)	4m 9s
test (windows-latest, x64, 1.6)	11m 27s
test (windows-latest, x64, nightly)	9m 35s
test (windows-latest, x86, 1.6)	13m 46s
test (windows-latest, x86, nightly)	14m 44s
	1h 9m 15s

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