ttrss: Ensure that database is removed after uninstall

- Setting ttrss/purge to 'true' in debconf is not retrained after the package
has been install. So, set it again just before package removal.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/ttrss/__init__.py

@@ -120,6 +120,11 @@ class TTRSSApp(app_module.App):
         if not old_version:
             self.enable()
 
+    def uninstall(self):
+        """De-configure and uninstall the app."""
+        privileged.uninstall()
+        super().uninstall()
+
     def force_upgrade(self, packages):
         """Force update package to resolve conffile prompts."""
         if 'tt-rss' not in packages:

plinth/modules/ttrss/privileged.py

@@ -171,3 +171,11 @@ def load_augeas():
     aug.set('/augeas/load/Phpvars/incl[last() + 1]', DATABASE_FILE)
     aug.load()
     return aug
+
+
+@privileged
+def uninstall():
+    """Ensure that the database is removed."""
+    # This setting set before deb package installation is not retrained,
+    # somehow.
+    action_utils.debconf_set_selections(['tt-rss tt-rss/purge boolean true'])