s390/fpu: Remove comment about TIF_FPU

It has been removed in commit 2c6b9676 ("s390/fpu: remove TIF_FPU"),
so we should not mention TIF_FPU in the comment here anymore. Since the
remaining parts of the comment just document the obvious fact that
save_user_fpu_regs() saves the FPU state, simply remove the comment now
completely.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20240503080648.81461-1-thuth@redhat.com


Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>