typing: suppress error of py2 encoding.strtolocal() and .strfromlocal()

I don't know how to conditionally get rid of these py2/py3 overloads from
.pyi file. Instead, this patch makes pytype ignore the false-positives:

  line 271, in strtolocal: bad option in return type [bad-return-type]
  Expected: bytes
  Actually returned: str

mercurial/encoding.py

@@ -268,11 +268,11 b' else:'
 
     def strtolocal(s):
         # type: (str) -> bytes
-        return s
+        return s  # pytype: disable=bad-return-type
 
     def strfromlocal(s):
         # type: (bytes) -> str
-        return s
+        return s  # pytype: disable=bad-return-type
 
     strmethod = pycompat.identity