test: drop state from AsyncSaga constructor params

This uses the real rootReducer to populate the initial state in the test
AsyncSaga. This way we don't have to populate default values. Since it
isn't used often, we can omit the parameter and just call the updateState()
method after creating the object if modifications are needed.

src/explorer/sagas.test.ts

@@ -21,7 +21,7 @@ describe('handleExplorerImportFiles', () => {
         const testFileName = 'test.py';
         const testFileContents = '# test';
 
-        const saga = new AsyncSaga(explorer, { fileStorage: { fileNames: [] } });
+        const saga = new AsyncSaga(explorer);
 
         jest.spyOn(browserFsAccess, 'fileOpen').mockResolvedValueOnce([
             mock<FileWithHandle>({