[REM] packaging: add sassc to the rpm package

Since 565277ac sassc is used as a
fallback when the python libsass is not available.

With this commit, the saasc package dependency is added to the rpm to
avoid installing libsass with pip.

setup.cfg

@@ -5,7 +5,7 @@ post-install = setup/redhat/postinstall.sh
 
 requires =
   babel
-  libsass
+  sassc
   libxslt-python
   pychart
   pyparsing

setup/redhat/postinstall.sh

@@ -59,4 +59,3 @@ KillMode=mixed
 [Install]
 WantedBy=multi-user.target
 EOF
-pip3 install libsass