fix(pack): remove automatic @deno/shim-deno injection (#34411)
`@deno/shim-deno` is not actively maintained and slipped into the 2.8.0
release as an automatic dependency injected by `deno pack` whenever
it detected Deno API usage in the packed source. Packages that use
Deno APIs should not silently gain an unmaintained polyfill as a
transitive runtime dependency.
Remove the AST-based Deno usage detector, the `--no-deno-shim` flag
(its opt-out), the shim import injection, and the `@deno/shim-deno`
entry in the generated `package.json`. The four spec tests that
exercised shim behaviour are deleted as well.
