Issues with major-mode-remap-defaults

[Tim Ruffing]

Emacs 30.0.93 (and maybe earlier versions of Emacs 30) initialize
major-mode-remap-defaults with mappings from the built-in modes to the
AUCTeX modes: 

See lisp/textmodes/tex-mode.el around line 1041
(Or, brace yourself, click that link to GitHub:  
https://github.com/emacs-mirror/emacs/blob/68bcabf58afddb377d172857ce7648ad3ff09618/lisp/textmodes/tex-mode.el#L1041-L1045
)

AUCTeX does the opposite. This means that after loading AUXTeX, we'll
get this "funny" value for major-mode-remap-defaults:

((doctex-mode . docTeX-mode)
 (latex-mode . LaTeX-mode)
 (texinfo-mode . Texinfo-mode)
 (plain-tex-mode . plain-TeX-mode)
 (tex-mode . TeX-tex-mode)
 (LaTeX-mode . latex-mode)
 (plain-TeX-mode . plain-tex-mode)
 (TeX-mode . tex-mode))

Now this is full chaos. If you set latex-mode in auto-mode-alist,
you'll get LaTeX-mode, and the other way around. (I mean, at least
Emacs stops after one remapping and doesn't enter infinite loop.)

I think AUCTeX should just remove the built-in mappings, which are
intended for the case where AUCTeX is not installed. Note that even
AUCTeX adds LaTeX-mode entries to auto-mode-alist that will now be
redirected to latex-mode.

Best,
Tim

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