Cleanup list of LaTeX packages

[tarleb]

This adds lua-ul, which is required for underlined text in LuaLaTeX.

Removed: cmap and pdflscape. Not sure why those where in there in the first place.

[tarleb]

I've revised this further, and the following packages are now removed as well:

• embedfile
• hyperxmp
• makecmds
• polyglossia
• xkeyval

Polyglossia was used upto pandoc 2.15, while embedfile and hyperxmp are useful when creating PDF/A files, but are not required. The other packages were dependencies.

[tarleb]

I think we should follow the principle that only necessary packages are included in the latex images.

I'm therefore going ahead with these changes, but we can revert them if someone disagrees.