RectAreaLightHelper missing update method or docs are wrong

[greggman]

Describe the bug

The docs for RectAreaLightHelper say there is an update function but no such function exists in the implementation of RectAreaLightHelper

To Reproduce

See Links above

Code

N/A

Live example

N/A

Expected behavior

Either an update method is added (would make it consistent with other helpers?) or the method is removed from the docs

Screenshots

N/A

Platform:

• Device: Desktop, Mobile
• OS: Windows, MacOS, Linux, Android, iOS
• Browser: Chrome, Firefox, Safari, Edge
• Three.js version: [dev, r126]

[Mugen87]

I guess it was missed to remove the method in #21016.

[greggman]

Should probably be added to the migration guide too?

3238bc3#diff-1c1f50f55edacb560f5ece578d841569c21fb0562fdcb1bcd92c34a6295e4053

[Mugen87]

Done!