[PyTorch Edge] Reduce dispatch table size further for a trimmed build (#66112)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66112
Eliminate Metal and Vulkan Dispatch Keys.
Test Plan: Build + Sandcastle
Differential Revision: D31298307
fbshipit-source-id: 31302fc626382db7997e5058750fa85458c9cbc1
