um: Remove unused ipi_pipe field from cpuinfo_um

It's no longer used after the removal of the SMP implementation in
TT mode by commit 28fa468 ("um: Remove broken SMP support").

While at it, remove the outdated comment.

Signed-off-by: Tiwei Bie <[email protected]>
Signed-off-by: Johannes Berg <[email protected]>

Author: btw616

arch/um/include/asm/processor-generic.h

@@ -71,7 +71,6 @@ extern void start_thread(struct pt_regs *regs, unsigned long entry,
 
 struct cpuinfo_um {
 	unsigned long loops_per_jiffy;
-	int ipi_pipe[2];
 	int cache_alignment;
 	union {
 		__u32		x86_capability[NCAPINTS + NBUGINTS];

arch/um/kernel/um_arch.c

@@ -54,12 +54,9 @@ static void __init add_arg(char *arg)
 
 /*
  * These fields are initialized at boot time and not changed.
- * XXX This structure is used only in the non-SMP case.  Maybe this
- * should be moved to smp.c.
  */
 struct cpuinfo_um boot_cpu_data = {
 	.loops_per_jiffy	= 0,
-	.ipi_pipe		= { -1, -1 },
 	.cache_alignment	= L1_CACHE_BYTES,
 	.x86_capability		= { 0 }
 };