title: delete an array element inside array of array
body: <p>Hi I am trying to delete an element which is inside array of array.
  my schema is :</p>
  
  <pre><code>var mySchema = Schema({ 
    primaryField:String,
    list1: [{
      item1: String,
      item2:String
    }],
    list2 : [{
    item3:String,
      item4 : [String]//item4 is string values available in item1
    }]
  });
  </code></pre>
  
  <p>for ex:</p>
  
  <pre><code>{
    "primaryField": "abc",
    "list1": [{
      "item1": "aa",
      "item2": "mystring"
    },{
      "item1": "bb",
      "item2": "sampStr"
    }],
    "list2": [{
      "item3": "stringitem",
      "item4": ["aa", "bb"]
    },{
      "item3": "sample",
      "item4": ["bb"]
    },{
      "item3": "samplestring",
      "item4": ["aa"]
    }]
  }
  </code></pre>
  
  <p>I have to delete the <code>"aa"</code> items from <code>list1</code> and the occurence of <code>"aa"</code> in <code>list2.item4</code> and if only <code>"aa"</code> is present in <code>item4</code> then i have to delete the entire object entry.</p>
  
  <p>my output should be:</p>
  
  <pre><code>{
    "primaryField": "abc",
    "list1": [{
      "item1": "bb",
      "item2": "sampStr"
    }],
    list2:[{
      "item3": "stringitem",
      "item4": ["bb"]
    },{
      "item3": "sample",
      "item4": ["bb"]
    }]
  }
  </code></pre>
  
  <p>could anyone help me to achieve this using node.js and mongoose. Schema cannot be modified.</p>