Pulls an item from an existing array

ExampleMongoDB$pullStatement.ts

/** create connection pool to system DB in MongoDB
* assume we are using https://www.npmjs.com/package/mongodb
* assume we begin with:
{
  system_id: 123,
  a: 1,
  b: 2,
  c: 3,
  watcher_emails: ['somebody@emailaddress.com']
}
*/

system_states_collection.update(
  { system_id: 123 },
  {
      $pull: {
          watcher_emails: 'somebody@emailaddress.com'
      }
  }
)
/** 
Resulting document: 
{
  system_id: 123,
  a: 4,
  b: 5,
  c: 3,
  watcher_emails: []
}
*/