Remove unnecessary TException.message hack

Thrift attempts to work-around the Python 2.7 DeprecationWarning
around `BaseException.message` by using a property.  This hack is
unnecessary since `message` is _also_ written as a regular attribute in
the `TException` constructor (and would be in any of its children),
hence the `BaseException_get_message()` wouldn't even be called.

This hack also stands in the way of making exception instances
immutable (which is a prerequisute to fixing THRIFT-4002).
diff --git a/lib/py/src/Thrift.py b/lib/py/src/Thrift.py
index c390cbb..b335bc1 100644
--- a/lib/py/src/Thrift.py
+++ b/lib/py/src/Thrift.py
@@ -90,15 +90,6 @@
 class TException(Exception):
     """Base class for all thrift exceptions."""
 
-    # BaseException.message is deprecated in Python v[2.6,3.0)
-    if (2, 6, 0) <= sys.version_info < (3, 0):
-        def _get_message(self):
-            return self._message
-
-        def _set_message(self, message):
-            self._message = message
-        message = property(_get_message, _set_message)
-
     def __init__(self, message=None):
         Exception.__init__(self, message)
         self.message = message