Remove deprecated "apple" Cargo feature #3340

Job	Run time
Check MSRV	57s
Lint macOS x86_64	3m 44s
Check formatting	11s
Lint iOS ARMv7s	3m 52s
Lint visionOS Aarch64 simulator	3m 49s
Lint GNUStep + exceptions	1m 28s
Lint header-translator	35s
Lint test-assembly	26s
Test macOS 15 Aarch64	1m 36s
Assembly tests	53s
Verify header translator output	2m 27s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Check framework features	0s
Test Compiler-RT	1m 40s
Test GNUStep with libobjc2 v1.9	1m 20s
Test GNUStep with libobjc2 v2.0	1m 19s
Compiler UI	49s
Test on iOS simulator w. dinghy	0s
Test GNUStep with libobjc2 v2.1 on nightly	1m 6s
Test GNUStep 32bit	1m 25s
	27m 37s

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