code: func (c *Collection) RemoveAll(selector interface{}) (info *ChangeInfo, err error) {
  	lerr, err := c.writeQuery(&deleteOp{c.FullName, selector, 0})
  	if err == nil && lerr != nil {
  		info = &ChangeInfo{Removed: lerr.N}
  	}
  	return info, err
  }
docs: // RemoveAll finds all documents matching the provided selector document
  // and removes them from the database.  In case the session is in safe mode
  // (see the SetSafe method) and an error happens when attempting the change,
  // the returned error will be of type *LastError.
  //
  // Relevant documentation:
  //
  //     http://www.mongodb.org/display/DOCS/Removing
  //