python 3.8 removed linux_distribution support completely and leaves that
functionality to third-party modules, which is provided by 'distro'.

Just completely remove the backwards compatibility and completely rely on that
module.

diff --git a/salt/grains/core.py b/salt/grains/core.py
index 04c1ae9..9280975 100644
--- a/salt/grains/core.py
+++ b/salt/grains/core.py
@@ -24,6 +24,7 @@ from errno import EACCES, EPERM
 import datetime
 import warnings
 import time
+from distro import linux_distribution
 
 # pylint: disable=import-error
 try:
@@ -35,23 +36,6 @@ except ImportError:
 __proxyenabled__ = ['*']
 __FQDN__ = None
 
-# Extend the default list of supported distros. This will be used for the
-# /etc/DISTRO-release checking that is part of linux_distribution()
-from platform import _supported_dists
-_supported_dists += ('arch', 'mageia', 'meego', 'vmware', 'bluewhite64',
-                     'slamd64', 'ovs', 'system', 'mint', 'oracle', 'void')
-
-# linux_distribution deprecated in py3.7
-try:
-    from platform import linux_distribution as _deprecated_linux_distribution
-
-    def linux_distribution(**kwargs):
-        with warnings.catch_warnings():
-            warnings.simplefilter("ignore")
-            return _deprecated_linux_distribution(**kwargs)
-except ImportError:
-    from distro import linux_distribution
-
 # Import salt libs
 import salt.exceptions
 import salt.log
@@ -1920,7 +1904,7 @@ def os_data():
         )
         (osname, osrelease, oscodename) = \
             [x.strip('"').strip("'") for x in
-             linux_distribution(supported_dists=_supported_dists)]
+             linux_distribution()]
         # Try to assign these three names based on the lsb info, they tend to
         # be more accurate than what python gets from /etc/DISTRO-release.
         # It's worth noting that Ubuntu has patched their Python distribution