Revert "[torchgen] Introduce Executorch types and signatures (#90591)"
This reverts commit ddf00c803b2a99f4eec8a040b53ee18f62800fdd.
Reverted https://github.com/pytorch/pytorch/pull/90591 on behalf of https://github.com/seemethere due to Part of a stack that causes internal failures, see https://www.internalfb.com/intern/sandcastle/job/4503600464398605/insights
