fix className leak

[JoviDeCroock]

Fixes #3159
Fixes #2582

I honestly think it's highly indeterministic to alter the props passed into a component, generally in React (compat) people will pas in either class or className and won't expect this to be changed. Introducing an additional prop is only going to confuse people. Note that we did not do this before

[coveralls]

Coverage remained the same at 99.624% when pulling 9be3898 on fix-class-leak into d744e24 on master.

[github-actions]

Size Change: 0 B

Total Size: 42 kB

Filename	Size	Change
compat/dist/compat.module.js	3.42 kB	-1 B
compat/dist/compat.umd.js	3.49 kB	+1 B

ℹ️ View Unchanged

Filename	Size	Change
compat/dist/compat.js	3.44 kB	0 B
debug/dist/debug.js	2.99 kB	0 B
debug/dist/debug.module.js	2.98 kB	0 B
debug/dist/debug.umd.js	3.07 kB	0 B
devtools/dist/devtools.js	232 B	0 B
devtools/dist/devtools.module.js	241 B	0 B
devtools/dist/devtools.umd.js	308 B	0 B
dist/preact.js	3.96 kB	0 B
dist/preact.min.js	3.98 kB	0 B
dist/preact.module.js	3.98 kB	0 B
dist/preact.umd.js	4.03 kB	0 B
hooks/dist/hooks.js	1.13 kB	0 B
hooks/dist/hooks.module.js	1.14 kB	0 B
hooks/dist/hooks.umd.js	1.2 kB	0 B
jsx-runtime/dist/jsxRuntime.js	317 B	0 B
jsx-runtime/dist/jsxRuntime.module.js	327 B	0 B
jsx-runtime/dist/jsxRuntime.umd.js	395 B	0 B
test-utils/dist/testUtils.js	437 B	0 B
test-utils/dist/testUtils.module.js	439 B	0 B
test-utils/dist/testUtils.umd.js	515 B	0 B

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[marvinhagemeister]

Awesome 🙌

[nullpaper]

As a heads up this breaks Router5 <Link> component styles and presumably any React components that are expecting a className prop but getting a preact class. In short:

// Preact `10.5.15`
<Link class='green' />
// -> <a class='green' /> 
// -> WORKS! 🎉

// Preact `10.6.0` (ths PR)
<Link class='green' />
// -> <a />
// -> No class propagation 💥

This is a breaking change for a whole class of components.