docs: sysctl/kernel: remove rtsig entries

These have no corresponding code in the kernel.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/sysctl/kernel.rst

@@ -900,16 +900,6 @@ ROM/Flash boot loader. Maybe to tell it what to do after
 rebooting. ???
 
 
-rtsig-max & rtsig-nr
-====================
-
-The file rtsig-max can be used to tune the maximum number
-of POSIX realtime (queued) signals that can be outstanding
-in the system.
-
-rtsig-nr shows the number of RT signals currently queued.
-
-
 sched_energy_aware
 ==================