revert: Access data files from source folder (#1969)

[stevenjoezhang]

What does it do?

reverts #1969
fixes #5260

Motivation for the modification: I suspect that this feature is rarely used (I noticed it for the first time today). In fact, users can access the 'site' variable through the template engine, without the need for tags within the article.

Screenshots

Pull request tasks

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

[github-actions]

How to test

git clone -b data https://github.com/hexojs/hexo.git
cd hexo
npm install
npm test

[coveralls]

coverage: 99.529% (-0.001%) from 99.53% when pulling 74b514b on data into 3059fa0 on v7.0.0.

[D-Sketon]

breaking change？
maybe adding a parameter to control this behavior is a better choice?

[stevenjoezhang]

Yes, it is a breaking change, we could include it in the v7.0.0 release. However, I don't think it's necessary to add a new option. This usage is not mentioned in Hexo's documentation; it's a completely undocumented interface. We don't need to consider its stability and compatibility.