rpm: remove commented out rpm macro

Just commenting out macro isn't enough - % sequences are still
processed. Remove it completely, as it is already provided in build
environment.

rpm_spec/core-dom0.spec

@@ -23,8 +23,6 @@
 #
 #
 
-#%{!?python3_sitelib: %define python3_sitelib %(%{__python3} -c "from distutils.sysconfig import get_python_lib; print get_python_lib(False)")}
-
 %{!?version: %define version %(cat version)}
 
 # debug_package hack should be removed when BuildArch:noarch is enabled below