Remove special handling for LuaTeX in \genfrac

[zauguin]

READ ME FIRST: Please understand that in most cases we will not be able to merge a pull request because there are a lot of internal activities needed when updating the LaTeX2e sources. If you have a code suggestion please discuss it with the team first.

In \genfrac there is special handling for XeTeX and LuaTeX to avoid \overwithdelims and friends. The LuaTeX replacement is provided since "the relevant font dimen parameters are often not set in luatex as there are no matching values in the OpenType Math table". The replacement code conditionally uses the relevant font dimensions and tries to fallback to other logic if they are unset. The fallback code is completely broken. Triggering it manually fails with ! Missing font identifier since a scaling factor is passed when a font identifier is expected. Looking at the git history suggests that it never worked. We could try to fix it, but since noone complained about \binom and friends being completely broken in LuaTeX in the last decade it seems safe to assume that the font parameter is always set in practice. Therefore we can use \overwithdelims and friends directly. (Also if the font parameter does turn out to be missing in many cases we can start generating it in luaotfload.)

Internal housekeeping

Status of pull request

• Ready to merge

Checklist of required changes before merge will be approved

• n/a Test file(s) added
• Version and date string updated in changed source files
• Relevant \changes entries in source included
• Relevant changes.txt updated
• Rollback provided (if necessary)?
• ltnewsX.tex (and/or latexchanges.tex) updated

[mbertucci47]

This would be related to #432 I suppose