Moved version info from setup.cfg into package

It is better to make setup.cfg infer version info from the package
instead of vice versa.

Previous method only works where the package is "installed".
It doesn't work if we were to use this as a git submodule or frozen
environments like nuitka.

Author: vinayinvicible

oauth2_provider/__init__.py

@@ -1,9 +1,3 @@
-try:
-    from importlib.metadata import version
-except ImportError:
-    from importlib_metadata import version
-
-
-__version__ = version("django-oauth-toolkit")
+__version__ = "1.5.0"
 
 default_app_config = "oauth2_provider.apps.DOTConfig"

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = django-oauth-toolkit
-version = 1.5.0
+version = attr: oauth2_provider.__version__
 description = OAuth2 Provider for Django
 long_description = file: README.rst
 long_description_content_type = text/x-rst
@@ -36,7 +36,6 @@ install_requires =
 	requests >= 2.13.0
 	oauthlib >= 3.1.0
 	jwcrypto >= 0.8.0
-	importlib-metadata; python_version < "3.8"
 
 [options.packages.find]
 exclude = tests