The root fiber doesn't have a parent from which we can read the
`subtreeTag`, so we need to check its `effectTag` directly.
The root fiber previously did not have any pending passive effects,
but it does now that deleted fibers are cleaned up in the passive phase.
This allows us to remove a `schedulePassiveEffectCallback` call from the
synchronous unmount path.
Co-authored-by: Brian Vaughn <bvaughn@fb.com>
Andrew ClarkandBrian Vaughn
6ef997b534