fix(latex): disable smartparens pairs handled by AucTeX

[real-or-random]

• I searched the issue tracker and this hasn't been PRed before.
• My changes are not on the do-not-PR list for this project.
• My commits conform to Doom's git conventions.
• My changes are visual; I've included before and after screenshots.
• I am blindly checking these off.
• Any relevant issues or PRs have been linked to.
• This a draft PR; I need more time to finish it.

Sorry, I had to skip the linter again. It claims that "latex" is not a valid scope. (Or is anything wrong with my commit messages?!) Perhaps a bug introduced by ed9190e?

---

This disables smartparens pairs for quotation marks, which are broken.
Before this commit, typing a LaTeX comment

    % "Foo"

inserted

    % ''Foo`|`''

where | indicates the position of the cursor (wtf!).

Let's better AucTeX's support for quotation marks for now and accept
that the user won't get automatic insertions of closing quotation marks.

This also removes a wrong comment mentioning the non-existing variable
`+latex-enable-plain-double-quotes'.

[hlissner]

LGTM! Thanks again for your help!

Sorry, I had to skip the linter again. It claims that "latex" is not a valid scope. (Or is anything wrong with my commit messages?!) Perhaps a bug introduced by ed9190e?

This is a regression from 1adc318; I moved the linter's rules out into a new dotfile, but haven't yet backported the parts responsible for reading .doom! I'll deal with that soon. Until then, feel free to ignore its warnings about scopes.