use SvelteKit packaging features and remove Gro's

[ryanatkn]

The current SvelteKit integration overrides svelte-kit package, but we want Gro to do as little as necessary. Right now, tasks like gro build, gro deploy, and gro publish duplicate some of SvelteKit's functionality.

Gro's packaging has worked pretty well for TypeScript and Svelte libraries -- it publishes sourcemaps and typemaps for a nice editor experience. (e.g. vscode navigates to the source files on "go to definition") Defining a library is pretty nice too IMO: https://github.com/feltcoop/felt/blob/main/src/gro.config.ts

related:

• #333