bug#49306: 28.0.50; Info of Eshell/Extension Modules/* is empty

[Gabriel]

Emacs 28 from master branch (HEAD 8ebd8e1fea1d0d925850db97b64bf13a6a1f698b)

1. Open Info (C-h i)
2. Search for Eshell (C-s Eshell)
3. Navigate to 'Extension modules'
4. All child pages are empty:
   * Writing a module
   * Module testing
   * Directory handling
   * Key rebinding:
   * Smart scrolling
   * Terminal emulation

I checked the git history of file 'doc/misc/eshell.texi' and indeed
these sections are empty.

I suggest to either document these sections or remove these entries from
Info to avoid confusion.