Accepting request 869221 from home:lnussel:usrmove

- fix update-alternatives usage. Needs to be in %postun according to
  https://en.opensuse.org/openSUSE:Packaging_Multiple_Version_guidelines#update-alternatives_mechanism

OBS-URL: https://build.opensuse.org/request/show/869221
OBS-URL: https://build.opensuse.org/package/show/Base:System/gawk?expand=0&rev=82

gawk.spec

@@ -89,8 +89,8 @@ ln -s %{_sysconfdir}/alternatives/awk.1%{?ext_man} %{buildroot}%{_mandir}/man1/a
   --slave %{_mandir}/man1/awk.1.gz awk.1%{?ext_man} %{_mandir}/man1/gawk.1%{?ext_man}
 %endif
 
-%preun
-if [ $1 -eq 0 ]; then
+%postun
+if [ ! -f %{_bindir}/gawk ]; then
     %{_sbindir}/update-alternatives --remove awk %{_bindir}/gawk
 fi