Remove redundant handler check in Bus

[yatki]

Expected behavior

Bus doesn't know about the handler of the action. So we shouldn't have that check in the bus.

Actual behavior

That check is actually causing false exceptions.

lisk-sdk/framework/src/controller/bus.js

Lines 132 to 141 in 9f60bbe

	Object.keys(actions).forEach(actionName => {
	const actionFullName = `${moduleAlias}:${actionName}`;
	if (
	typeof actions[actionName] !== 'object' ||
	!actions[actionName].handler
	) {
	throw new Error(
	`Action "${actionFullName}" should be object with handler property.`
	);
	}

Steps to reproduce

Which version(s) does this affect? (Environment, OS, etc...)

2.0.0