undo change in files.py; to be addressed in separate PR

Author: poke1024

mathics/builtin/files.py

@@ -793,7 +793,8 @@ def apply(self, channel, expr, evaluation):
         expr = expr.get_sequence()
         expr = Expression('Row', Expression('List', *expr))
 
-        text = evaluation.format_output(from_python(expr), 'text')
+        evaluation.format = 'text'
+        text = evaluation.format_output(from_python(expr))
         stream.write(six.text_type(text) + '\n')
         return Symbol('Null')