Refactor examples.js to use async/await

[Swapnil-2001]

Fixes #1693

I have verified that this pull request:

• has no linting errors (npm run lint)
• is from a uniquely-named feature branch and has been rebased on top of the latest develop branch. (If I was asked to make more changes, I have made sure to rebase onto develop then too)
• is descriptively named and links to an issue number, i.e. Fixes #123

@catarak please let me know if the changes are okay.

[catarak]

Thanks for working on this! Your changes look great. One thing I would also suggest changing is the reliance on the library async (and the function eachSeries) which is used to make using callback functions easier. I believe you could get rid of it and just use the library q!

[Swapnil-2001]

Okay, I'll be changing that!

[Swapnil-2001]

Could you please go through the changes? This is my first time working with the library q so I'm not 100% sure!

[catarak]

Looking at this again, I also noticed that the mongoose queries (e.g. User.findOne) use callbacks—could these use async/await as well?

[Swapnil-2001]

Of course!

Also, I replaced remove with deleteOne, since remove is deprecated.