Mutator.close() has to be moved to @FinishBundle in WriteFn and DeleteFn

Since writer.close() contains a business logic and @TearDown is not guaranteed to call, it must be moved to @FinishBundle. The same thing about DeleteFn.

Details are here:

https://lists.apache.org/thread.html/rfcc0df0c5d09699033662c0eb8bcc86de9cc5b4923a50da81700569d%40%3Cdev.beam.apache.org%3E