Reapply "refactor(nix): nix-filter -> lib.fileset"

After extensive (5 minutes) of testing, it seems we don't actually come
across any Nix bugs with lib.fileset! (aside from those inherit to
it...but 🤷)

This reverts commit a49a58bc45.

Signed-off-by: Seth Flynn <getchoo@tuta.io>

flake.nix

@@ -16,8 +16,6 @@
       flake = false;
     };
 
-    nix-filter.url = "github:numtide/nix-filter";
-
     /*
       Inputs below this are optional and can be removed
 
@@ -44,7 +42,6 @@
       self,
       nixpkgs,
       libnbtplusplus,
-      nix-filter,
       ...
     }:
     let
@@ -100,7 +97,6 @@
         prismlauncher-unwrapped = prev.callPackage ./nix/unwrapped.nix {
           inherit
             libnbtplusplus
-            nix-filter
             self
             ;
         };