setup.py: switch import to setuptools

Switch to standard setuptools import, add suggested entries to
pyproject.toml.

Remove the --clean argument.  As the comment suggests I'm sure there
is history here, but having setup.py remove parts of the package does
not seem like something required at this point.

Also clean up the imports to remove unused and group them together at
the top.

pyproject.toml

@@ -1,3 +1,7 @@
+[build-system]
+requires = ["setuptools", "wheel"]
+build-backend = "setuptools.build_meta"
+
 [tool.black]
 line-length = 79
 

setup.py

@@ -35,10 +35,10 @@ import os
 import sys
 import time
 import warnings
-import datetime
-import tempfile
 import subprocess
 
+from setuptools import setup
+
 warnings.filterwarnings('always', category=DeprecationWarning)
 
 debug = '--debug' in sys.argv
@@ -97,55 +97,12 @@ if sys.version_info < (3, 6, 0) \
     sys.stderr.write('====================================================\n')
     time.sleep(60)
 
-import textwrap
-
-clean = False
-while '--clean' in sys.argv:
-    clean = True
-    sys.argv.remove('--clean')
-
-import glob
-import shutil
-import os
-
-
 plugins = [s for s in os.listdir('plugins') if
            os.path.exists(os.path.join('plugins', s, 'plugin.py'))]
 
 def normalizeWhitespace(s):
     return ' '.join(s.split())
 
-try:
-    from distutils.core import setup
-    from distutils.sysconfig import get_python_lib
-except ImportError as e:
-    s = normalizeWhitespace("""Supybot requires the distutils package to
-    install. This package is normally included with Python, but for some
-    unfathomable reason, many distributions to take it out of standard Python
-    and put it in another package, usually caled 'python-dev' or python-devel'
-    or something similar. This is one of the dumbest things a distribution can
-    do, because it means that developers cannot rely on *STANDARD* Python
-    modules to be present on systems of that distribution. Complain to your
-    distribution, and loudly. If you how much of our time we've wasted telling
-    people to install what should be included by default with Python you'd
-    understand why we're unhappy about this.  Anyway, to reiterate, install the
-    development package for Python that your distribution supplies.""")
-    sys.stderr.write(os.linesep*2)
-    sys.stderr.write(textwrap.fill(s))
-    sys.stderr.write(os.linesep*2)
-    sys.exit(-1)
-
-
-if clean:
-    previousInstall = os.path.join(get_python_lib(), 'supybot')
-    if os.path.exists(previousInstall):
-        try:
-            print('Removing current installation.')
-            shutil.rmtree(previousInstall)
-        except Exception as e:
-            print('Couldn\'t remove former installation: %s' % e)
-            sys.exit(-1)
-
 packages = ['supybot',
             'supybot.locales',
             'supybot.utils',