Remove unnecesary assert statement

Author: hwalinga

pandas/core/computation/expr.py

@@ -163,7 +163,6 @@ def _preparse(source, f=_compose(_replace_locals, _replace_booleans,
     the ``tokenize`` module and ``tokval`` is a string.
     """
     assert callable(f), 'f must be callable'
-    assert callable(g), 'g must be callable'
     return tokenize.untokenize(lmap(f, tokenize_string(g(source))))