linuxkpi: Use pageproc instead of vmproc

According to markj@:
pageproc contains the page daemon and laundry threads, which are
responsible for managing the LRU page queues and writing back dirty
pages.  vmproc's main task is to swap out kernel stacks when the system
is under memory pressure, and swap them back in when necessary.  It's a
somewhat legacy component of the system and isn't required.  You can
build a kernel without it by specifying "options NO_SWAPPING" (which is
a somewhat misleading name), in which vm_swapout_dummy.c is compiled
instead of vm_swapout.c.

Based on this, we want pageproc to emulate kswapd, not vmproc.

Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D18061

sys/compat/linuxkpi/common/include/linux/swap.h

@@ -45,7 +45,8 @@ get_nr_swap_pages(void)
 static inline int
 current_is_kswapd(void)
 {
-	return vm_curproc_is_vmproc();
+
+	return (curproc == pageproc);
 }
 
 #endif

sys/vm/vm_pageout.h

@@ -107,7 +107,5 @@ void vm_pageout_oom(int shortage);
 void vm_swapout_run(void);
 void vm_swapout_run_idle(void);
 
-bool vm_curproc_is_vmproc(void);
-
 #endif /* _KERNEL */
 #endif	/* _VM_VM_PAGEOUT_H_ */

sys/vm/vm_swapout.c

@@ -961,10 +961,3 @@ swapout(struct proc *p)
 	p->p_swtick = ticks;
 	return (0);
 }
-
-/* Used to determine if the current process is itself the reaper. */
-bool
-vm_curproc_is_vmproc(void)
-{
-	return curproc == vmproc;
-}