Remove reference cpp(1) which is not used anymore

usr.bin/calendar/calendar.1

@@ -28,7 +28,7 @@
 .\"     @(#)calendar.1  8.1 (Berkeley) 6/29/93
 .\" $FreeBSD$
 .\"
-.Dd April 6, 2013
+.Dd July 24, 2016
 .Dt CALENDAR 1
 .Os
 .Sh NAME
@@ -295,7 +295,6 @@ This is no longer true, the date is only recognized when it occurs
 at the beginning of a line.
 .Sh SEE ALSO
 .Xr at 1 ,
-.Xr cpp 1 ,
 .Xr mail 1 ,
 .Xr cron 8
 .Sh HISTORY