dillon1000/react

[Flight fixture] Remove redundant `use` (#26373)

Now that promises are renderable nodes, we can remove the `use` call
from the root of the Flight fixture.

Uncached promises will likely be accompanied by a warning when they are
rendered outside a transition. But this promise is the result of a
Flight response, so it's cached. And it's also a rendered as part of a
transition. So it's fine. Indeed, this is the canonical way to use this
feature.