pyloxi: use OFClass directly

It now includes everything we need except pyname.
diff --git a/py_gen/templates/_unpack.py b/py_gen/templates/_unpack.py
index 81efb21..c3d3fd3 100644
--- a/py_gen/templates/_unpack.py
+++ b/py_gen/templates/_unpack.py
@@ -53,6 +53,6 @@
         obj.${m.name} = ${gen_unpack_expr(m.oftype, reader_expr, version=version)}
 ::     #endif
 :: #endfor
-:: if ofclass.has_external_alignment or ofclass.has_internal_alignment:
+:: if ofclass.params.get('length_includes_align') != None:
         reader.skip_align()
 :: #endif