all: remove nix mentions

Hakurei is no longer developed on nixos, and the nix deployment method
has been removed upstream. This change updates the website to reflect
these changes.

static/install.html

@@ -36,10 +36,7 @@
 
             <p>Hakurei can be installed to almost any Linux-based operating system by running
             <code>install.sh</code> from a release tarball found <a
-            href="https://git.gensokyo.uk/rosa/hakurei/releases" target="_blank">here</a>.
-            With that said, the current easiest method for using Hakurei with desktop apps would be
-            via the <a href="https://git.gensokyo.uk/rosa/hakurei/src/branch/master/options.md"
-            target="_blank">companion NixOS module</a>.</p>
+            href="https://git.gensokyo.uk/rosa/hakurei/releases" target="_blank">here</a>.</p>
 
             <p>We strongly recommend using one of the official installation methods. Third party
             installation guides tend to be out-of-date and often contain misguided advice and