pfctl(8): Remove superflous parenthesis

Since apropos(8) uses case-insensitive regular expressions by default
for both manpage names and descriptions, pfctl appears in results
regardless of the parenthetical initialism.

MFC after:      1 week
Reported by:	ziaee@

sbin/pfctl/pfctl.8

@@ -29,7 +29,7 @@
 .Os
 .Sh NAME
 .Nm pfctl
-.Nd control the packet filter (PF) device
+.Nd control the packet filter device
 .Sh SYNOPSIS
 .Nm pfctl
 .Bk -words