Latex fixes

[dschrempf]

Hi! This fixes #1100; well, it disables some features of smartparens for latex modes. The PR also includes some other nits and changes. Let me know if I should exclude those.

Finally, this change is a breaking change for people using

(sp-local-pair modes "``" nil ...))) ;; or
(sp-local-pair modes "`" nil ...)))

For example, this affects Doom Emacs, which I am using. The corresponding patch for Doom Emacs is attached.
s.patch

[Fuco1]

Hmm, to be fair though, the "default" behaviour is fine until you use those special language quotes, right? I wonder if we shouldn't keep it working e.g. in english.

[dschrempf]

For me, smartparens is completely broken in LaTeX, also in English. I am not using German in my documents. It could be a Doom Emacs issue. I removed all the relevant changes (see the patch), but who knows.