[turbopack] Remove LocalTaskType::Native, it is dead (#85480)
### What
Remove `LocalTaskType::Native` and supporting infrastructure. Simplify schedule_local_task to remove an allocation and `CaptureFuture`.
### Why?
local tasks for things other than 'resolve' tasks have been proven to not be a very useful idea. However, for resolve tasks they do still make sense. We can use the small amount of indirection provided by `LocalTask` to optimize how we launch other turbotasks.
Now that the local task implementation is clearly just about turbo-tasks infrastructure (rather than calling arbitrary 'user code') we can simplify dispatching a bit.
