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

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

hgext/schemes.py

@@ -159,7 +159,7 b' def extsetup(ui):'
         else:
             hg.repo_schemes[scheme] = ShortRepository(url, scheme, t)
 
-    extensions.wrapfunction(urlutil, b'hasdriveletter', hasdriveletter)
+    extensions.wrapfunction(urlutil, 'hasdriveletter', hasdriveletter)
 
 
 @command(b'debugexpandscheme', norepo=True)