Fix unload plugins behavior without filelists

For packages originating outside the System repository, we don't populate the `pkg.files` when running without filelists metadata. Use RPM database as a source instead.

dnf/plugin.py

@@ -29,6 +29,7 @@
 import logging
 import operator
 import os
+import rpm
 import sys
 import traceback
 
@@ -193,7 +194,7 @@ def unload_removed_plugins(self, transaction):
 
  # check whether removed plugin file is added at the same time (upgrade of a plugin)
  for pkg in transaction.install_set:
- erased_plugin_files.difference_update(pkg.files)
+ erased_plugin_files.difference_update(pkg._header[rpm.RPMTAG_FILENAMES])
 
  # unload plugins that were removed in transaction
  for plugin_file in erased_plugin_files: