Remove keyczar from test-requirements.txt since this is py27 only

Remove keyczar from test-requirements.txt since this is only required for unit tests for python 2.7.

Author: m4dcoder

test-requirements.txt

@@ -28,9 +28,4 @@ webtest==2.0.25
 rstcheck>=3.3.1,<3.4
 tox==3.14.1
 pyrabbit
-# Since StackStorm v2.8.0 we now use cryptography instead of keyczar, but we still have some tests
-# which utilize keyczar and ensure new cryptography code is fully compatible with keyczar code
-# (those tests only run under Python 2.7 since keyczar doesn't support Python 3.x).
-# See https://github.com/StackStorm/st2/pull/4165
-python-keyczar
 pip-tools  # For pip-compile, to check for version conflicts