Remove duplicate fixture.ts files once fast-tooling no longer pulls packages from npm registry

[chrisdholt]

As part of the vNext updates, the fast-tooling package was updated to pull dependencies from NPM to avoid issues and breaking changes. As part of this, we needed to remove the internal dependency on the local fast-foundation fixture utility and duplicate the those files within tooling.

This issue exists to track the removal of these duplicated files once tooling is again taking its dependency from within the repository.

[janechu]

We're going to keep this as a duplicate file, due to the potential for this breaking in the future, as well as the issue of this not being consumer-friendly as it is not documented in any meaningful way.