fix(sqllab): Allow clear on schema and catalog (apache#32515)

Author: justinpark

superset-frontend/src/components/DatabaseSelector/index.tsx

@@ -406,6 +406,7 @@ export default function DatabaseSelector({
         options={catalogOptions}
         showSearch
         value={currentCatalog || undefined}
+        allowClear
       />,
       refreshIcon,
     );
@@ -432,6 +433,7 @@ export default function DatabaseSelector({
         options={schemaOptions}
         showSearch
         value={currentSchema}
+        allowClear
       />,
       refreshIcon,
     );