repoview: use class literal for creating filteredchangelog

The type name is constant, so we don't need to create it dynamically
using type(). As suggested by Yuya.

Differential Revision: https://phab.mercurial-scm.org/D7364

mercurial/repoview.py

@@ -227,9 +227,10 b' def wrapchangelog(unfichangelog, filtere'
     cl = copy.copy(unfichangelog)
     cl.filteredrevs = filteredrevs
 
-    cl.__class__ = type(
-        'filteredchangelog', (filteredchangelogmixin, cl.__class__), {}
-    )
+    class filteredchangelog(filteredchangelogmixin, cl.__class__):
+        pass
+
+    cl.__class__ = filteredchangelog
 
     return cl