code: public boolean removeTransactionAware(TransactionAware txAware) {
      Preconditions.checkState(currentTx == null, "Cannot remove TransactionAware while there is an active transaction.");
      return txAwares.remove(txAware);
    }
docs: Removes a {@link TransactionAware} and withdraws from participation in the transaction.
  Withdrawal is only allowed if there is no active transaction.
  
  @param txAware the {@link TransactionAware} to be removed
  @return true if the given {@link TransactionAware} is removed; false otherwise.
  @throws IllegalStateException if there is an active transaction going on with this TransactionContext.