Don't call UnwatchBlocking unconditionally

[dranikpg]

Based on #1387

Currently if BLPOP was awakened, it sill calls UnwatchBlocking -> UnwatchShardCb, but with expired = false. All that gets executed is the following:

  // Need to see why I decided to call this.
  // My guess - probably to trigger the run of stalled transactions in case
  // this shard concurrently awoke this transaction and stalled the processing
  // of TxQueue.
  shard->PollExecution("unwatchcb", nullptr);

Do we really need this hop if immediately after the action hop follows? I highly suspect that's not the case