Changed naming of flags.

Made sure legacy import is also still ok

nominatim/clicmd/args.py

@@ -87,8 +87,7 @@ class NominatimArgs:
     offline: bool
     ignore_errors: bool
     index_noanalyse: bool
-    only_import_data: bool
-    only_prepare_database: bool
+    prepare_database: bool
 
     # Arguments to 'index'
     boundaries_only: bool