Remove SvelteKit as a dependency

[hobbes7878]

Contingent on undertaking #69, we may want to make this a Svelte-only library.

Non-SvelteKit projects have problems with SvelteKit stores like $app/... and this library.

There are cases like the current SREPs Vite-based rig that don't use SvelteKit and there may be more in the future for slimmed down, single-page rigs. (Thinking our current homepage, which uses sapper now and may continue to need something that can compile down to a legacy bundle.)

Main breaking change would be that users will need to construct paths, e.g. with $assets store, before passing them into components like SEO.

[hobbes7878]

Noting #72 as a good example of not relying on SvelteKit deps.