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.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

Documentation/arch/arm64/sve.rst

@@ -117,11 +117,6 @@ the SVE instruction set architecture.
 * The SVE registers are not used to pass arguments to or receive results from
   any syscall.
 
-* In practice the affected registers/bits will be preserved or will be replaced
-  with zeros on return from a syscall, but userspace should not make
-  assumptions about this.  The kernel behaviour may vary on a case-by-case
-  basis.
-
 * All other SVE state of a thread, including the currently configured vector
   length, the state of the PR_SVE_VL_INHERIT flag, and the deferred vector
   length (if any), is preserved across all syscalls, subject to the specific