gitweb: Don't backup/restore a drop-in configuration file

- /etc/gitweb-freedombox.conf is a drop-in configuration file. It is provide in
/usr and linked into /etc/. It is overwritten when freedombox package is
upgraded. So, it is incorrect to backup/restore the file.

Tests:

- Run functional tests that include backup/restore.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Veiko Aasa <veiko17@disroot.org>

plinth/modules/gitweb/manifest.py

@@ -2,7 +2,6 @@
 
 from django.utils.translation import gettext_lazy as _
 
-CONFIG_FILE = '/etc/gitweb-freedombox.conf'
 GIT_REPO_PATH = '/var/lib/git'
 REPO_DIR_OWNER = 'www-data'
 
@@ -33,11 +32,4 @@ clients = [
     },
 ]
 
-backup = {
-    'config': {
-        'files': [CONFIG_FILE]
-    },
-    'data': {
-        'directories': [GIT_REPO_PATH]
-    }
-}
+backup = {'data': {'directories': [GIT_REPO_PATH]}}