Build: remove ipa.pot from Git as it can be re-generated at any time

All the source files are in the very same repo so there is no point
in keeping the file in Git.

https://fedorahosted.org/freeipa/ticket/6418

Reviewed-By: Martin Basti <mbasti@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Lukas Slebodnik <lslebodn@redhat.com>

.gitignore

@@ -5,6 +5,7 @@
 /ABOUT-NLS
 /po/*.gmo
 /po/*~
+/po/ipa.pot
 /po/Makefile.hack
 /po/Makefile.in.in
 /po/Makevars.template