Update doc/po/**/*.po files.

[omasanori]

Note that it is just an update using po4a, so reduction of untranslated entries using msgattrib (discussed on #11383) is not yet available.

[alexcrichton]

I thought we were going to remove all the generated portions of these files? Did msgattrib turn out to be insufficient?

[omasanori]

@alexcrichton Yes, I think we reached an agreement with removal.

I thought that a normal update before starting working in a new method might be needed for translator if it takes some time before the new one works.
However, I got second thoughts that currently translation is not so active and Japanese only, so update is not useful and borrows precious time of bors. I'm sorry. Closing.

[alexcrichton]

Oh no worries! If it takes awhile to get the slimmed down versions working, we can certainly reconsider merging updated translations.

[omasanori]

OK, I'll try to solve the problem this weekend. If I become aware that it is more difficult than I've thought, then I'll send fat update PR again. Thank you.