[SSR v2] Fix unused imports from '@lwc/ssr-runtime'

[nolanlawson]

In core, this Rollup warning is treated as an error:

LWC1002: Error in module resolution: "api", "track" and "wire" are imported from external
module "@lwc/ssr-runtime" but never used in `foo.js`

This happens because sometimes we are sloppy about doing e.g.:

import { api } from '@lwc/ssr-runtime'

... in the output .js files from the @lwc/ssr-compiler, even though api may be unused.

We should clean this up and ensure that all of our imports are actually used.

[git2gus]

This issue has been linked to a new work item: W-17152250