stringutil: remove Python 2 support code

Differential Revision: https://phab.mercurial-scm.org/D12314

mercurial/utils/stringutil.py

@@ -964,6 +964,4 b' def parselist(value):'
 def evalpythonliteral(s):
     """Evaluate a string containing a Python literal expression"""
     # We could backport our tokenizer hack to rewrite '' to u'' if we want
-    if pycompat.ispy3:
         return ast.literal_eval(s.decode('latin1'))
-    return ast.literal_eval(s)