fix: return callback if called

[curbengh]

What does it do?

fix remaining alerts of lgtm.

• file.js - since options is not used in the function, there's no need to handle it.
• tag.js - return a callback if render() is called with a callback.

How to test

git clone -b callback-handling https://github.com/curbengh/hexo.git
cd hexo
npm install
npm test

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[SukkaW]

SInce Promise.fromCallback is used, is it still necessary to use asCallback?

hexo/test/scripts/extend/tag.js

Lines 167 to 178 in 0fd5736

	it('render() - callback', () => {
	const tag = new Tag();
	const callback = spy();
	tag.register('test', () => 'foo');
	return tag.render('{% test %}', callback()).then(result => {
	result.should.eql('foo');
	callback.calledOnce.should.be.true;
	});
	});

callback related test case is already added and it seems passed.