[LyX/master] Remove hebrew letter document class

[Udicoudco]

On Wed, Jun 12, 2024 at 6:42 AM Udicoudco <udifoglle at gmail.com> wrote:
>
> On Wed, Jun 12, 2024 at 3:07 AM Richard Kimberly Heck
> <rikiheck at gmail.com> wrote:
> > In this case,
> > removing this file will prevent a document that uses it from loading
> > properly, let alone compiling. So we keep it and mark it obsolete.
>
> A document that directly uses this layout from the settings
> will be loaded with the letter layout, and the LaTeX export,
> and as a consequence the pdf output will stay identical.
> This is why I did the format change in this commit.

Briefly looking in lyx_2_4.py there are several format changes
which are dependent on the value of document.textclass,
so they have the same flaw as in my commit, i.e. they don't catch
the case of a custom user layout file that input the layout file
related to said format change.