remove TeX manual, it moved to https://gitlab.com/fdroid/fdroid-website
The whole TeX manual has been folded into the new Jekyll-based website (once fdroid-website!29 (merged) is merged), so the old TeX manual is no longer needed at all. This should remove all traces of it from fdroidserver so that people don't get confused by where the docs actually are.
You can see a live copy of the new website here: https://fdroid.gitlab.io/fdroid-website/docs/