title: How can I delete result of list query in one step?
body: <p>I've tried this to delete <code>operations</code> where product ID equals to <code>myProdID</code>.
  It deleted whole operations branch, not just ones equal to query result.</p>
  
  <pre><code>this.af.database.list('operations', {
          query: {
            orderByChild: 'products/productID',
            equalTo: myProdID
          }
        }).remove();
  </code></pre>
  
  <p>What shall I use in order to do it in one line of code and not run for loop to remove each item? .map ?</p>