DEPR-15: Remove usage of firebase-token-generator

The old Notes Django app is the only caller of this no longer
supported library. I have verified that this old app is no
longer functional and is already slated to be removed as part
of DEPR-18.

So this commit simply removes the call to firebase-token-generator
and leaves removal of the Notes app to DEPR-18.

common/lib/xmodule/xmodule/annotator_token.py

@@ -1,35 +0,0 @@
-"""
-This file contains a function used to retrieve the token for the annotation backend
-without having to create a view, but just returning a string instead.
-
-It can be called from other files by using the following:
-from xmodule.annotator_token import retrieve_token
-"""
-from __future__ import absolute_import
-
-import datetime
-
-from firebase_token_generator import create_token
-
-
-def retrieve_token(userid, secret):
-    '''
-    Return a token for the backend of annotations.
-    It uses the course id to retrieve a variable that contains the secret
-    token found in inheritance.py. It also contains information of when
-    the token was issued. This will be stored with the user along with
-    the id for identification purposes in the backend.
-    '''
-
-    # the following five lines of code allows you to include the default timezone in the iso format
-    # for more information: http://stackoverflow.com/questions/3401428/how-to-get-an-isoformat-datetime-string-including-the-default-timezone
-    dtnow = datetime.datetime.now()
-    dtutcnow = datetime.datetime.utcnow()
-    delta = dtnow - dtutcnow
-    newhour, newmin = divmod((delta.days * 24 * 60 * 60 + delta.seconds + 30) // 60, 60)
-    newtime = "%s%+02d:%02d" % (dtnow.isoformat(), newhour, newmin)
-    # uses the issued time (UTC plus timezone), the consumer key and the user's email to maintain a
-    # federated system in the annotation backend server
-    custom_data = {"issuedAt": newtime, "consumerKey": secret, "userId": userid, "ttl": 86400}
-    newtoken = create_token(secret, custom_data)
-    return newtoken

common/lib/xmodule/xmodule/tests/test_annotator_token.py

@@ -1,26 +0,0 @@
-"""
-This test will run for annotator_token.py
-"""
-from __future__ import absolute_import
-
-import unittest
-
-from xmodule.annotator_token import retrieve_token
-
-
-class TokenRetriever(unittest.TestCase):
-    """
-    Tests to make sure that when passed in a username and secret token, that it will be encoded correctly
-    """
-
-    def test_token(self):
-        """
-        Test for the token generator. Give an a random username and secret token,
-        it should create the properly encoded string of text.
-        """
-        expected = "eyJhbGciOiAiSFMyNTYiLCAidHlwIjogIkpXVCJ9.eyJpc3N1ZWRBdCI6ICIyMDE0LTAyLTI3VDE3OjAwOjQyLjQwNjQ0MSswOjAwIiwgImNvbnN1bWVyS2V5IjogImZha2Vfc2VjcmV0IiwgInVzZXJJZCI6ICJ1c2VybmFtZSIsICJ0dGwiOiA4NjQwMH0.Dx1PoF-7mqBOOSGDMZ9R_s3oaaLRPnn6CJgGGF2A5CQ"
-        response = retrieve_token("username", "fake_secret")
-
-        # because the middle hashes are dependent on time, conly the header and footer are checked for secret key
-        self.assertEqual(expected.split('.')[0], response.split('.')[0])
-        self.assertNotEqual(expected.split('.')[2], response.split('.')[2])