Delete outdated translated copies of developer guide

[seanbudd]

Link to issue number:

Closes #13333

Summary of the issue:

There are two unmaintained files, which are translated versions of the developer guide.
These have been unmaintained for over a decade.

Description of user facing changes

None

Description of development approach

Remove files

[SaschaCowley]

Is it worth removing the developerGuide option from l10nUtil? I assume it can't be removed from md2html though?

[seanbudd]

I'm not sure i understand l10nUtil enough to be sure. @michaelDCurran ?

[CyrilleB79]

I have no problem with deletion of these outdated files.

Please note, though that some people have expressed the desire to keep the possibility to have the dev guide translatable (cc @tiago-casal and also @michaelDCurran for the thread on translators mailing list).

It probably applies to a very small minority of languages, but we should keep tracking this request somewhere, or, if it is finally decided not to make the dev guide translatable, clarify this decision on the translators mailing list for complete information.
Thanks.