Delete .nvmrc (#30765)

Summary:
Tiny PR that removes an old orphaned `.nvmrc` file (added in 2018 and not touched since then).

Most likely the project does not work with Node.js 8.11.3 anymore. There is (no longer) a need to attempt to strictly enforce a specific version client-side. `package.json` _already_ declares
```
"node": ">=12"
```
in the `engines` section, so we should be good.

## Changelog

[General] [Removed] - Delete .nvmrc

Pull Request resolved: #30765

Test Plan: Nothing to test...

Reviewed By: hramos

Differential Revision: D26190114

Pulled By: TheSavior

fbshipit-source-id: 515807da8a9e28fd28c12e8b5416ed125436341c