Remove warning for dangling passive effects

[acdlite]

In legacy mode, a test can get into a situation where passive effects are "dangling" — an update finished, and scheduled some passive effects, but the effects don't flush.

This is why React warns if you don't wrap updates in act. The act API is responsible for flushing passive effects. But there are some cases where the act API (in legacy roots) intentionally doesn't warn, like updates that originate from roots and classes. It's possible those updates will render children that contain useEffect. Because of this, dangling effects are still possible, and React doesn't warn about it.

So we implemented a second act warning for dangling effects. The warning was never part of a public release. It was only enabled in concurrent roots.

However, in concurrent roots, we now enforce that all APIs that schedule React work must be wrapped in act. There's no scenario where dangling passive effects can happen that doesn't already trigger the warning for updates. So the dangling effects warning is redundant.

So we can delete it.

[sizebot]

Comparing: d5b6b4b...975c75c

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	130.19 kB	130.19 kB	=	41.42 kB	41.41 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	135.16 kB	135.16 kB	=	42.95 kB	42.95 kB
facebook-www/ReactDOM-prod.classic.js	=	419.90 kB	419.90 kB	=	77.34 kB	77.33 kB
facebook-www/ReactDOM-prod.modern.js	=	408.48 kB	408.48 kB	=	75.59 kB	75.59 kB
facebook-www/ReactDOMForked-prod.classic.js	=	419.90 kB	419.90 kB	=	77.34 kB	77.34 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 975c75c

[salazarm]

nice