Remove support for 'python setup.py test'

[jamadden]

That has fallen out of favor in recent times and many other zopefoundation packages have dropped support. There's a whole raft of support code cluttering setup.py that could be removed, and it doesn't test anything that uses layers (which is a lot). Plus it doesn't even work as it is:

$ python setup.py test
running test
running egg_info
writing top-level names to src/ZODB.egg-info/top_level.txt
writing entry points to src/ZODB.egg-info/entry_points.txt
writing dependency_links to src/ZODB.egg-info/dependency_links.txt
writing requirements to src/ZODB.egg-info/requires.txt
writing src/ZODB.egg-info/PKG-INFO
reading manifest file 'src/ZODB.egg-info/SOURCES.txt'
reading manifest template 'MANIFEST.in'
warning: no previously-included files found matching '.coveragerc'
warning: no previously-included files found matching '.travis.yml'
warning: no previously-included files found matching 'appveyor.yml'
warning: no previously-included files found matching 'buildout.cfg'
warning: no previously-included files matching '*.dll' found anywhere in distribution
warning: no previously-included files matching '*.pyo' found anywhere in distribution
warning: no previously-included files matching '*.so' found anywhere in distribution
warning: no previously-included files matching '*~' found anywhere in distribution
writing manifest file 'src/ZODB.egg-info/SOURCES.txt'
running build_ext
Traceback (most recent call last):
  File "setup.py", line 147, in <module>
    python_requires='>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*',
  File "/lib/python2.7/site-packages/setuptools/__init__.py", line 140, in setup
    return distutils.core.setup(**attrs)
  File "//lib/python2.7/distutils/core.py", line 151, in setup
    dist.run_commands()
  File "/lib/python2.7/distutils/dist.py", line 953, in run_commands
    self.run_command(cmd)
  File "/lib/python2.7/distutils/dist.py", line 972, in run_command
    cmd_obj.run()
  File "//lib/python2.7/site-packages/setuptools/command/test.py", line 228, in run
    self.run_tests()
  File "//lib/python2.7/site-packages/setuptools/command/test.py", line 250, in run_tests
    exit=False,
  File "//lib/python2.7/unittest/main.py", line 94, in __init__
    self.parseArgs(argv)
  File "//lib/python2.7/unittest/main.py", line 149, in parseArgs
    self.createTests()
  File "//lib/python2.7/unittest/main.py", line 158, in createTests
    self.module)
  File "//lib/python2.7/unittest/loader.py", line 130, in loadTestsFromNames
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/lib/python2.7/unittest/loader.py", line 115, in loadTestsFromName
    test = obj()
  File "setup.py", line 88, in alltests
    _unittests_only(suite, mod.test_suite())
AttributeError: 'module' object has no attribute 'test_suite'