Remove dependency `autorest`

Remove any dependencies, direct or indirect, on autorest and related packages.

This tool uses autorest to generate a "merge" JSON file and a sourcemap file, and the tool itself supports comparing either a single JSON file, or merging all the JSON files from a version tag.

However, the specs repo "Breaking Changes" currently only uses the feature to compare single files. At one time, it had code to use the feature to merge files, but it was removed in 2022 for unclear reasons (something related to false positives with deleted swaggers).

In either case, it might be relatively easy to use a different library or custom code, to replace `autorest` which is only used for this purpose.