requireArrowFunctions: only check for FunctionExpression as a callback?

[hzoo]

Similar to #1413

So I think we can only warn when using FunctionExpression as a callback since in all the other cases we would have to do work to check for this/scope.

So in my next PR I would make an exception for node.parent.type === 'VariableDeclarator' or ReturnStatement

Or maybe since its only one case now it should somehow only check if it's a callback (!node.parent)?