Remove node storage used for test

[antho1404]

A ./scratch directory is created even when the LocalStorageStore is not used.

https://github.com/xmtp/xmtp-js/blob/a7263d74a290f72b4faa0057a27d8463728272f6/src/store/LocalStorageStore.ts#L3

This is fine for development mode and/or tests but creates an issue for any SSR application running on a read-only environment like vercel.

We should be able to initialize a client even in an SSR environment without any error.

Here is the error from a deployment on Vercel

[neekolas]

This is removed