Remove out-of-date translated docs

[MasterOdin]

The es, fr, and jp translations, while nice to have in theory, are so far out of date to probably be detrimental. Without either a larger contributor community around phinx, or a regular maintainer willing to dedicate to maintaining these docs, I see no reason to keep them and let them grow more and more out of date.

As such, this PR removes the pages as well as building them altogether from phinx. While it's regrettable, at least no one will risk getting docs that are flat out wrong for something phinx does or supports.

[dereuromark]

I am fine with it, but we also need to ask the rest of the team here.

[aspirantzhang]

I have seen that .rst files can be translated "line by line" using .po files. I think this is a good solution. I wonder why CakePHP doesn't take this approach?
However, in the process of working with Chinese documents, I also found that files in other languages were missing a lot of content, so it might be a good idea to delete them all.

[markstory]

I have seen that .rst files can be translated "line by line" using .po files. I think this is a good solution. I wonder why CakePHP doesn't take this approach?

The main reason I didn't go down this path was having to sync every update made to the english docs to all the po files. I wanted the docs to be 'easy' to contribute to, and trying to convince occasional contributors to also update a PO file didn't feel like a smooth process. Using PO files doesn't address the content going out of date either, so it felt like a lot of extra work for little benefit.

I also found that files in other languages were missing a lot of content, so it might be a good idea to delete them all.

If the docs are outdated and we have no maintainers, removing the docs translations is reasonable. Better that folks use google translate to view the content vs reading potentially wrong information.