Fix build by adding Requires on python2-devel

Additionally, remove bogus python_sitelib macro redefinition.

gnome-doc-utils.spec

@@ -1,5 +1,3 @@
-%{!?python_sitelib: %define python_sitelib %(%{__python} -c "from distutils.sysconfig import get_python_lib; print get_python_lib(0)")}
-
 Name: gnome-doc-utils
 Version: 0.20.10
 Release: 16%{?dist}
@@ -18,7 +16,7 @@ BuildRequires:  gcc
 BuildRequires: libxml2-devel >= 2.6.12
 BuildRequires: libxslt-devel >= 1.1.8
 BuildRequires: python2-libxml2
-BuildRequires: python2
+BuildRequires: python2-devel
 BuildRequires: intltool
 BuildRequires: gettext
 BuildRequires: scrollkeeper