Drop dependencies on IPS from the RPM

As reported by @stdweird, the RPM depends wrongly on `perl(IPS)`, which is specific to Solaris.

This fix is based on [the Fedora recommendations](https://fedoraproject.org/wiki/Packaging:AutoProvidesAndRequiresFiltering#Perl).  I have tested it on Fedora, but I don't have any RH boxes anymore, so I don't know if it is compatible with the EL/SL versions of RPM.

I'd appreciate if somebody tested it for me. :smile: