py3: call codecs.escape_decode() directly

The same rule as 3b7a6941a6ef applies.

mercurial/util.py

@@ -2138,7 +2138,7 b' def escapestr(s):'
     return codecs.escape_encode(s)[0]
 
 def unescapestr(s):
-    return s.decode('string_escape')
+    return codecs.escape_decode(s)[0]
 
 def uirepr(s):
     # Avoid double backslash in Windows path repr()