sysctl: clean up nr_pdflush_threads leftover

nr_pdflush_threads has been long deprecated and
removed, but a remnant of its glorious past is
still around in CTL_VM names enum. This patch
is a minor clean-up to that case.
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/uapi/linux/sysctl.h

@@ -161,7 +161,7 @@ enum
 enum
 {
 	VM_UNUSED1=1,		/* was: struct: Set vm swapping control */
-	VM_UNUSED2=2,		/* was; int: Linear or sqrt() swapout for hogs */
+	VM_UNUSED2=2,		/* was: int: Linear or sqrt() swapout for hogs */
 	VM_UNUSED3=3,		/* was: struct: Set free page thresholds */
 	VM_UNUSED4=4,		/* Spare */
 	VM_OVERCOMMIT_MEMORY=5,	/* Turn off the virtual memory safety limit */
@@ -174,7 +174,7 @@ enum
 	VM_DIRTY_RATIO=12,	/* dirty_ratio */
 	VM_DIRTY_WB_CS=13,	/* dirty_writeback_centisecs */
 	VM_DIRTY_EXPIRE_CS=14,	/* dirty_expire_centisecs */
-	VM_NR_PDFLUSH_THREADS=15, /* nr_pdflush_threads */
+	VM_UNUSED15=15,		/* was: int: nr_pdflush_threads */
 	VM_OVERCOMMIT_RATIO=16, /* percent of RAM to allow overcommit in */
 	VM_PAGEBUF=17,		/* struct: Control pagebuf parameters */
 	VM_HUGETLB_PAGES=18,	/* int: Number of available Huge Pages */