MAINT: drop astropy TestRunner (deprecated) (#649)

* MAINT: drop astropy TestRunner (deprecated)

* drop os import

Author: rrjbca

skypy/_astropy_init.py

@@ -1,13 +1,8 @@
 # Licensed under a 3-clause BSD style license - see LICENSE.rst
-import os
 
-__all__ = ['__version__', 'test']
+__all__ = ['__version__']
 
 try:
     from .version import version as __version__
 except ImportError:
     __version__ = ''
-
-# Create the test function for self test
-from astropy.tests.runner import TestRunner
-test = TestRunner.make_test_runner_in(os.path.dirname(__file__))