Dev dependency declaration file appears in package

[dsherret]

@dsherret, with 0.43.1 the source maps are now gone, but this file still remains:

npm notice 6.2kB esm/deps/jsr.io/@hexagon/proper-tags/2.0.3-alpha.0/dist/proper-tags.d.ts

And since it's only a test dependency, it was not supposed to be included in the npm package.

You can easily reproduce this with https://github.com/felipecrs/jsonc-weaver:

$ git clone https://github.com/felipecrs/jsonc-weaver
$ cd jsonc-weaver
$ deno task build-npm
$ (cd npm && npm pack)

Originally posted by @felipecrs in #486