Remove old code import imp, old style trackers db/backend_name Module imp is depricated. Removing that means rewriting old style trackers that used imp to load schema and config files. So removed code supporting old style trackers that have been depricated since 2008. Added test to verify that existence of dbinit.py triggers alert that tracker is old style and not supported. Also remove support for depricated db/backend_name file for specifying backend. It is now specified in config.ini's [rdbms] backend. It looks like not specifying an [rdbms] backend key in config.ini throws a config error. However I left in a check and throw an exception with details if there is an empty backend value. But I don't think it will ever be triggered. Removed unused import of imp in a number of test files.

--- a/test/test_mailgw.py	Sun Dec 20 12:28:59 2020 -0500
+++ b/test/test_mailgw.py	Sun Dec 20 15:43:07 2020 -0500
@@ -13,7 +13,7 @@
 
 import email
 from . import gpgmelib
-import unittest, tempfile, os, shutil, errno, imp, sys, difflib, time, io
+import unittest, tempfile, os, shutil, errno, sys, difflib, time, io
 
 import pytest