Remove unsafe from unconditionally safe subgroup ops #541

Job	Run time
Test (macOS-latest)	7m 59s
cargo-deny	1m 3s
Compiletest (ubuntu-24.04)	8m 14s
Test (windows-2022)	15m 58s
Difftest (windows-2022)	16m 11s
Android (ubuntu-24.04, aarch64-linux-android)	8m 25s
Compiletest (windows-2022)	15m 48s
Compiletest (macOS-latest)	8m 27s
Difftest (ubuntu-24.04)	9m 11s
Test (ubuntu-24.04)	8m 28s
Difftest (macOS-latest)	8m 54s
Lint	6m 24s
test_success	3s
	1h 55m 5s

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