cputime: remove cputime_to_nsecs fallback

The archs that use cputime_to_nsecs() internally provide their own
definition and don't need the fallback. cputime_to_usecs() unused except
in this fallback, and is not defined anywhere.

This removes the final remnant of the cputime_t code from the kernel.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Link: https://lore.kernel.org/r/20221220070705.2958959-1-npiggin@gmail.com

arch/s390/kernel/idle.c

@@ -12,9 +12,9 @@
 #include <linux/notifier.h>
 #include <linux/init.h>
 #include <linux/cpu.h>
-#include <linux/sched/cputime.h>
 #include <trace/events/power.h>
 #include <asm/cpu_mf.h>
+#include <asm/cputime.h>
 #include <asm/nmi.h>
 #include <asm/smp.h>
 #include "entry.h"

arch/s390/kernel/vtime.c

@@ -7,13 +7,13 @@
  */
 
 #include <linux/kernel_stat.h>
-#include <linux/sched/cputime.h>
 #include <linux/export.h>
 #include <linux/kernel.h>
 #include <linux/timex.h>
 #include <linux/types.h>
 #include <linux/time.h>
 #include <asm/alternative.h>
+#include <asm/cputime.h>
 #include <asm/vtimer.h>
 #include <asm/vtime.h>
 #include <asm/cpu_mf.h>

include/linux/sched/cputime.h

@@ -8,15 +8,6 @@
  * cputime accounting APIs:
  */
 
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
-#include <asm/cputime.h>
-
-#ifndef cputime_to_nsecs
-# define cputime_to_nsecs(__ct)	\
-	(cputime_to_usecs(__ct) * NSEC_PER_USEC)
-#endif
-#endif /* CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
-
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
 extern bool task_cputime(struct task_struct *t,
 			 u64 *utime, u64 *stime);

kernel/sched/cputime.c

@@ -3,6 +3,10 @@
  * Simple CPU accounting cgroup controller
  */
 
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
+ #include <asm/cputime.h>
+#endif
+
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
 
 /*