Remove leftover Python 2 compatibility shim

In Python 3, __str__ should not return bytes.

Author: jdufresne

src/PIL/PdfParser.py

@@ -241,15 +241,11 @@ def __bytes__(self):
                 result.extend(make_bytes("#%02X" % b))
         return bytes(result)
 
-    __str__ = __bytes__
-
 
 class PdfArray(list):
     def __bytes__(self):
         return b"[ " + b" ".join(pdf_repr(x) for x in self) + b" ]"
 
-    __str__ = __bytes__
-
 
 class PdfDict(collections.UserDict):
     def __setattr__(self, key, value):