Add delete method for cookies

[mikeybinns]

I think we should add a delete method to cookies which just acts as a shortcut for serialising a cookie with an expires option set in the past.

await cookie.delete()
// is the same as
await cookie.serialize(null, {
  expires: new Date(1970, 0, 1),
})

This is easier to remember and easier to write and read for developers.
It would accept no value or options because if you're deleting the cookie, they don't matter.

[wong2]

May I ask why are you using expires instead of maxAge: -1?

[mikeybinns]

No particular reason, does the same thing, it's just a different method.

[wong2]

Thanks!