doc: rename x509.extKeyUsage to x509.keyUsage

[panva]

This partially reverts #50603. It keeps the description but reverts to use the actual property name. #50603 should not have landed.

node/lib/internal/crypto/x509.js

Lines 270 to 277 in 9bc923a

	get keyUsage() {
	let value = this[kInternalState].get('keyUsage');
	if (value === undefined) {
	value = this[kHandle].keyUsage();
	this[kInternalState].set('keyUsage', value);
	}
	return value;
	}