Allow non-LaTeX intermediaries for PDF generation

[ashi-agrawal]

As of pandoc 2.8.0.1, released in November 2019, pdf is a valid output format. Since well before then, LaTeX was not the only intermediary format for creating PDFs; we currently force latex as the intermediary, which poses problems when trying to use a different intermediary format.

To fix this, we should be able to remove this line and actually use pdf as the output format. I've tested this locally to use typst as an intermediary, which previously failed with the failure pdf-engine typst is not compatible with output format latex but now correctly invokes and passes through the pandoc arguments.

[JessicaTegner]

Sounds like a good idea, since pandoc does support it.
Feel free to open a pr for it @ashi-agrawal then we can test it on CI to make sure nothing breaks :)

[ashi-agrawal]

Great - just opened a PR. Thanks!