meta: Drop tectonic

It's better to be pragmatic here and not choose tectonic when texlive
works extremely well and without any of the problems one would encounter
with tectonic.

The future of tectonic is unfortunately a mystery as well, due to the
status of the GitHub repository and its dependence on the unmaintained
XeTeX.

See: https://tex.stackexchange.com/questions/593031/what-are-the-downsides-of-using-xetex/593217#593217

modules/shell.nix

@@ -109,7 +109,6 @@ in
           clippy
           nodejs
           deno
-          tectonic
           ;
       })
     ];