Simplify the closing of the bidi reactor now that we are using a more modern version of GRPC.
Simplify the closing of the bidi reactor now that we are using a more modern version of GRPC.

PiperOrigin-RevId: 376788691
Change-Id: Ie3cdff2b0c2bfeb360d9f583b1c31e7018c64210

deepmind/reverb,deepmind/reverb,deepmind/reverb,deepmind/reverb