remove xgetdomainname module from Gnulib?

[Paul Eggert]

While looking into memory allocation issues I noticed the xgetdomainname 
module. As far as I know, nobody uses it, so I propose we remove it. The 
getdomainname function is used for the NIS domain name, and few programs 
would need that nowadays, as the world has mostly moved on to LDAP etc.

xgetdomainname was written by Simon Josefsson. I checked the GNU 
programs I thought he might be contributing to (GnuTLS, libtasn1, 
nettle, Emacs, inetutils) and xgetdomainname doesn't seem to be used 
there any more.