lib/installation: Always prune on updating unless the NO_PULL flag is set

The current condition being checked to decide when to prune after updating
a flatpak from the public API is probably not the best one, since NO_DEPLOY
doesn't imply that prunable objects will be available, as that's something
that depends on whether a pull operation is performed, not a deployment.

So, change that condition so that we now always prune after updating unless
a NO_PULL flag has been explicitly set, which means that no prunable objects
would be available and so it's safe to ignore that step.

https://github.com/flatpak/flatpak/issues/1703

Closes: #1704
Approved by: alexlarsson

lib/flatpak-installation.c

@@ -1897,7 +1897,8 @@ flatpak_installation_update_full (FlatpakInstallation    *self,
   if (result == NULL)
     goto out;
 
-  if ((flags & FLATPAK_UPDATE_FLAGS_NO_DEPLOY) != 0)
+  /* We don't get prunable objects if not pulling */
+  if (!(flags & FLATPAK_UPDATE_FLAGS_NO_PULL))
     flatpak_dir_prune (dir_clone, cancellable, NULL);
 
 out: