wrapfunction: use sysstr instead of bytes as argument in "beautifygraph"

This is as valid and simpler, it will help us to eventually get ride of
`safehasattr`.

hgext/beautifygraph.py

@@ -103,5 +103,5 b' def extsetup(ui):'
         )
         return
 
-    extensions.wrapfunction(graphmod, b'outputgraph', outputprettygraph)
-    extensions.wrapfunction(templatekw, b'getgraphnode', getprettygraphnode)
+    extensions.wrapfunction(graphmod, 'outputgraph', outputprettygraph)
+    extensions.wrapfunction(templatekw, 'getgraphnode', getprettygraphnode)