Mark elf2aout as deprecated.

Only sparc64 used this, so we will be removing it from FreeBSD 13. Add
the usual deprecation notice in a MFC-able way.

Reviewed by: emaste, rgrimes
Differential Revision: https://reviews.freebsd.org/D23526

usr.bin/elf2aout/elf2aout.1

@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd December 23, 2008
+.Dd February 6, 2020
 .Dt ELF2AOUT 1
 .Os
 .Sh NAME
@@ -46,6 +46,12 @@ and this utility is designed to accommodate.
 If
 .Ar infile
 is not in ELF format, an error message will be presented.
+.Sh DEPRECATION NOTICE
+The
+.Nm
+utility is not present in
+.Fx 13.0
+and later.
 .Sh SEE ALSO
 .Xr elf 3 ,
 .Xr a.out 5