Historically we have relied on intltool to install a standard
po/Makefile.in.in which has very limited scope for customization.
intltool is deprecated in favour of standard gettextize tools,
but these share the same disadvantages.

Writing make rules for po file management is no more difficult
than any other rules libvirt-glib has, so stop using intltool
and don't use gettextize ether.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>