docs: Remove reference to removed CBE_CPUFREQ_SPU_GOVERNOR

Remove a reference to CBE_CPUFREQ_SPU_GOVERNOR which has been removed.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20241218105523.416573-20-mpe@ellerman.id.au

Author: mpe

Documentation/admin-guide/kernel-per-CPU-kthreads.rst

@@ -278,12 +278,7 @@ To reduce its OS jitter, do any of the following:
 		due to the rtas_event_scan() function.
 		WARNING:  Please check your CPU specifications to
 		make sure that this is safe on your particular system.
-	e.	If running on Cell Processor, build your kernel with
-		CBE_CPUFREQ_SPU_GOVERNOR=n to avoid OS jitter from
-		spu_gov_work().
-		WARNING:  Please check your CPU specifications to
-		make sure that this is safe on your particular system.
-	f.	If running on PowerMAC, build your kernel with
+	e.	If running on PowerMAC, build your kernel with
 		CONFIG_PMAC_RACKMETER=n to disable the CPU-meter,
 		avoiding OS jitter from rackmeter_do_timer().