Remove %clean section

None of currently supported distributions need that.
Last one was EL5 which is EOL for a while.

Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

python-isodate.spec

@@ -110,9 +110,6 @@ popd
 %{__python2} -c 'import setuptools; execfile("setup.py")' install --skip-build --root %{buildroot}
 %endif
 
-%clean
-rm -rf %{buildroot}
-
 %check
 %{__python2} setup.py test