Do not hardcode the warning filter

The application should control whether warnings should be visible or not. By
hardcoding the simplefilter we turn on warnings' visibility for all modules
that follow. Removing this allows the application code to decide if warnings
should be shown.

To enable warnings through the command line pass -Wd to the python interpreter.

Quoting the python warnings module documentation[0]:
> You can do this from the command-line by passing -Wd to the interpreter (this
> is shorthand for -W default). This enables default handling for all warnings,
> including those that are ignored by default. To change what action is taken
> for encountered warnings you simply change what argument is passed to -W,
> e.g. -W error. See the -W flag for more details on what is possible.

  [0]: https://docs.python.org/2/library/warnings.html#updating-code-for-new-versions-of-python

Signed-off-by: Ivan Kanakarakis <ivan.kanak@gmail.com>

Author: c00kiemon5ter

src/saml2/aes.py

@@ -8,8 +8,6 @@
     'It will be removed in the next version. '
     'Use saml2.cryptography.symmetric instead.'
 ).format(name=__name__, type='module')
-
-_warnings.simplefilter('default')
 _warnings.warn(_deprecation_msg, DeprecationWarning)
 
 

src/saml2/authn.py

@@ -1,4 +1,4 @@
-import warnings
+import warnings as _warnings
 import logging
 import six
 import time
@@ -15,7 +15,6 @@
 __author__ = 'rolandh'
 
 logger = logging.getLogger(__name__)
-warnings.simplefilter('default')
 
 
 class AuthnFailure(SAMLError):
@@ -130,7 +129,7 @@ def aes(self):
             'This attribute is deprecated. '
             'It will be removed in the next version. '
             'Use self.symmetric instead.')
-        warnings.warn(_deprecation_msg, DeprecationWarning)
+        _warnings.warn(_deprecation_msg, DeprecationWarning)
         return self.symmetric
 
     def __call__(self, cookie=None, policy_url=None, logo_url=None,

src/saml2/cryptography/symmetric.py

@@ -13,9 +13,6 @@
 import cryptography.hazmat.primitives.ciphers as _ciphers
 
 
-_warnings.simplefilter('default')
-
-
 class Default(object):
     """The default symmetric cryptography method."""