python-mako: use BBCLASSEXTEND instead of native recipe

There isn't a need for a separate native recipe, so use BBCLASSEXTEND and
overrides.

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>

meta-oe/recipes-devtools/python/python-mako_0.7.2.bb

@@ -17,3 +17,6 @@ RDEPENDS_${PN} = "python-threading \
                   python-netclient \
                   python-html \
 "
+RDEPENDS_${PN}_class-native = ""
+
+BBCLASSEXTEND = "native nativesdk"