Remove NSObject special-casing #3137

Job	Run time
Check MSRV	46s
Lint macOS x86_64	2m 30s
Check formatting	11s
Lint iOS ARMv7s	2m 48s
Lint visionOS Aarch64 simulator	2m 17s
Lint GNUStep + exceptions	1m 27s
Lint header-translator	38s
Lint test-assembly	24s
Test macOS 15 Aarch64	1m 23s
Verify header translator output	53s
Compiler UI	42s
Assembly tests	50s
Check framework features	0s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Test Compiler-RT	21s
Test GNUStep with libobjc2 v1.9	1m 27s
Test GNUStep with libobjc2 v2.0	1m 1s
Test on iOS simulator w. dinghy	0s
Test GNUStep with libobjc2 v2.1 on nightly	2m 16s
Test GNUStep 32bit	1m 21s
	21m 15s

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