arm64/sve: Remove bitrotted comment about syscall behaviour

arm64/sve: Remove bitrotted comment about syscall behaviour

When we documented that we always clear state not shared with FPSIMD we
didn't catch all of the places that mentioned that state might not be
cleared, remove a lingering reference.

Reported-by: Edmund Grimley-Evans <edmund.grimley-evans@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240124-arm64-sve-sme-doc-v2-1-fe3964fb3c19@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>