Take the slide fonts from TeX Live rather than the tree

Open Sans and Roboto Mono ship in texlive-fonts-extra, which the other
templates already require. LuaLaTeX resolves them by family name through
luaotfload, which indexes the TeX tree, so the vendored copies and their
relative Path= keys are unnecessary.

Same faces, pixel-identical output.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

slides_template/fonts.tex

@@ -1,19 +1,7 @@
-% Font setup shared by the slides and by the notes pages that mknotes
-% typesets, so that the two match. Loaded by example.tex directly and passed
-% to mknotes with --preamble.
-%
-% Requires fontspec, which unicode-math pulls in on the slides side. Paths must
-% stay relative to the document directory: LuaTeX fails to resolve a
-% parent-relative Path= and dies with an unhelpful empty-filename error.
+% Shared by the slides and by the notes pages mknotes typesets, so the two
+% match. Both families come from texlive-fonts-extra.
 
-\setsansfont{OpenSans}[
-  Path = fonts/OpenSans/, Extension = .ttf,
-  UprightFont = *-Regular, BoldFont = *-Bold,
-  ItalicFont = *-Italic, BoldItalicFont = *-BoldItalic]
-
-\setmonofont{RobotoMono}[
-  Path = fonts/RobotoMono/, Extension = .ttf,
-  UprightFont = *-Regular, BoldFont = *-Bold,
-  ItalicFont = *-Italic, BoldItalicFont = *-BoldItalic]
+\setsansfont{Open Sans}
+\setmonofont{Roboto Mono}
 
 \renewcommand{\familydefault}{\sfdefault}