dillon1000/react

Remove `debugRenderPhaseSideEffects` flag (#17270)

There are two similar flags, `debugRenderPhaseSideEffects` and
`debugRenderPhaseSideEffectsForStrictMode`. The strict mode one is the
only one that is actually used. I think originally the theory is that
we would one day turn it on for all components, even outside strict
mode. But what we'll do instead is migrate everyone to strict mode.

The only place `debugRenderPhaseSideEffects` was being used was in
an internal test file. I rewrote those tests to use public APIs.