chore(deps): drop unused graphql-iso-date

[onpaws]

Discord discussion

Description

The motivation behind this one-liner PR mostly boils down to cleaning up what appears to be a spurious warning when running npm i --no-package-lock in projects consuming graphile-engine/PostGraphile.
Apologies if I'm wrong in my hypothesis - I acked through the repos for both graphile-engine as well as PostGraphile, looking for any instances of require() or import for this module and found no actual usages (only inside yarn.lock).

I happily defer to those smarter than me on this topic -- it would seem graphql-iso-date is going unused these days.
The module itself appears to be unmaintained since late 2018; the README steers users towards graphql-scalars.

Also it sounds like PostGraphile may already have this functionality anyway?

Here's the previous PR that touched this.

$ npm i --no-package-lock
npm WARN graphql-iso-date@3.6.1 requires a peer of graphql@^0.5.0 || ^0.6.0 || ^0.7.0 || ^0.8.0-b || ^0.9.0 || ^0.10.0 || ^0.11.0 || ^0.12.0 || ^0.13.0 || ^14.0.0 but none is installed. You must install peer dependencies yourself.

added 176 packages from 205 contributors and audited 178 packages in 6.233s

Performance impact

I would imagine that running npm install and possibly other things (e.g. app init) might be a tiny bit faster.

Security impact

This dependency doesn't appear to be getting used anyway, so it should be immaterial, AFAICT.

Checklist

• My code matches the project's code style and yarn lint:fix passes.

(Since this PR is a chore, the items under here seem irrelevant, but can expound more as desired)

• I've added tests for the new feature, and yarn test passes.
• I have detailed the new feature in the relevant documentation.
• I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• If this is a breaking change I've explained why.

[benjie]

I'm not sure we've ever needed this 😕