title: Remove attitributes not apart of an array MongoDB
body: <p>Due to some poorly planned code earlier on, my server added a lot of redundant attributes to log documents pushed to MongoDB. I'd like to roll through the entire database and $unset attributes that do not fit an approved list.</p>
  
  <p>So basically, if a document looks like this: </p>
  
  <pre><code>{
  _id: ...,
  content: ...,
  attr_sub: ...,
  attr_sub_0_attr_sub: ...,
  ...
  }
  </code></pre>
  
  <p>I want to match it with ["_id", "content", "attr_sub"], thus unsetting other attributes, and giving me:</p>
  
  <pre><code>{
  _id: ...,
  content: ...,
  attr_sub: ...
  }
  </code></pre>
  
  <p>For the life of me, I can't think of a way to do this, please tell me this is possible with mongodb conditions...</p>