Cleanup `skipCheckGenericClasses` #150

Job	Run time
Platform test (7.4)	2m 54s
Platform test (8.0)	3m 20s
Platform test (8.1)	2m 50s
Platform test (8.2)	3m 6s
Platform test (8.3)	2m 57s
Platform test (8.4)	2m 49s
Platform test (8.1, doctrine/orm:^3.0 doctrine/dbal:^4.0 carbonphp/carbon-doctrine-types:^3 gedmo...	2m 39s
Platform test (8.2, doctrine/orm:^3.0 doctrine/dbal:^4.0 carbonphp/carbon-doctrine-types:^3 gedmo...	2m 42s
Platform test (8.3, doctrine/orm:^3.0 doctrine/dbal:^4.0 carbonphp/carbon-doctrine-types:^3 gedmo...	3m 4s
Platform test (8.4, doctrine/orm:^3.0 doctrine/dbal:^4.0 carbonphp/carbon-doctrine-types:^3 gedmo...	2m 48s
	29m 9s

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