Fixed unexpected early-exit of settings sync

no issue

- `for .. of` loop contained a `return` rather than a `continue` so the whole function was being exited with an unexpected `undefined` return value after the first loop where an unknown setting is removed

ghost/custom-theme-settings-service/lib/service.js

@@ -134,7 +134,7 @@ module.exports = class CustomThemeSettingsService {
                 debug(`Removing custom theme setting '${theme.name}.${knownSetting.key}' - ${hasBeenRemoved ? 'not found in theme' : 'type changed'}`);
                 await this.repository.destroy({id: knownSetting.id});
                 removedIds.push(knownSetting.id);
-                return;
+                continue;
             }
 
             // replace value with default if it's not a valid select option