Remove unsafe from unconditionally safe subgroup ops #542

Job	Run time
Test (windows-2022)	16m 35s
Test (ubuntu-24.04)	7m 59s
Android (ubuntu-24.04, aarch64-linux-android)	8m 13s
Test (macOS-latest)	12m 31s
Difftest (ubuntu-24.04)	8m 34s
Lint	6m 26s
Compiletest (windows-2022)	4m 1s
Difftest (windows-2022)	17m 25s
Compiletest (ubuntu-24.04)	4m 12s
Difftest (macOS-latest)	8m 23s
Compiletest (macOS-latest)	3m 47s
cargo-deny	1m 11s
test_success	3s
	1h 39m 20s

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