refactor(turbo-tasks): Remove task id from RawVc::LocalOutput (#78561)
After https://github.com/vercel/next.js/pull/78488 and https://github.com/vercel/next.js/pull/78487, the task id isn't really needed anymore, so this removes it!
There's no expected change in memory consumption: `RawVc` is still 128 bits because `RawVc::TaskCell` is 96 bits, and the type is aligned to the nearest 64 bit machine word.