Unfork Substrait

### Description

The copy of Substrait has diverged from the source repository. Ideally the fork would be removed and the official version would be used directly.

The issue names no files, tests, or entry points. Inspect the repository for the copied Substrait source and its current linkage to the upstream repository, then determine whether the copy can be replaced by the official version; done means the fork is removed without breaking the project’s build or Substrait integration.

Written by the indexing model from the issue text.