Remove support for running Python on the mopidy/ dir

It doesn't make sense to run Mopidy without extensions registered, thus you'll
need to use setuptools and to run `python setup.py develop` anyway. Doing so
makes running `mopidy` from anywhere in the development virtualenv work,
removing any need for running `python mopidy/`.

mopidy/__main__.py

@@ -17,12 +17,6 @@ mopidy_args = sys.argv[1:]
 sys.argv[1:] = []
 
 
-# Add ../ to the path so we can run Mopidy from a Git checkout without
-# installing it on the system.
-sys.path.insert(
-    0, os.path.abspath(os.path.join(os.path.dirname(__file__), '../')))
-
-
 from mopidy import commands, ext
 from mopidy.audio import Audio
 from mopidy import config as config_lib

tests/help_test.py

@@ -12,7 +12,10 @@ class HelpTest(unittest.TestCase):
     def test_help_has_mopidy_options(self):
         mopidy_dir = os.path.dirname(mopidy.__file__)
         args = [sys.executable, mopidy_dir, '--help']
-        process = subprocess.Popen(args, stdout=subprocess.PIPE)
+        process = subprocess.Popen(
+            args,
+            env={'PYTHONPATH': os.path.join(mopidy_dir, '..')},
+            stdout=subprocess.PIPE)
         output = process.communicate()[0]
         self.assertIn('--version', output)
         self.assertIn('--help', output)