Fix the package declaration

Since isrcsubmit.py is currently contained in a single file, that means
package declaration is a bit different. Instead of specifying a
`packages` entry, we just mark the singular module file in `py_modules`
instead.

Note that the script still isn’t working, but that requires a bit more
refactoring, so that’ll be done in a separate commit.

Follow-up to 73c820d

setup.py

@@ -102,8 +102,12 @@ def run(self):
         url="https://github.com/JonnyJD/musicbrainz-isrcsubmit",
         requires=["discid(>=1.0.0)", "musicbrainzngs(>=0.4)"],
         python_requires='>=3.7',
-        packages=["isrcsubmit"],
-        scripts=["isrcsubmit.py"],
+        py_modules=["isrcsubmit"],
+        entry_points={
+            'console_scripts': [
+                'isrcsubmit.py=isrcsubmit:main',
+            ],
+        },
         license="GPLv3+",
         classifiers=[
             "Development Status :: 5 - Production/Stable",