refactor: remove a dead comment about GSK_RENDERER=cairo

hosts/common/programs/sane-theme.nix

@@ -335,16 +335,4 @@ in
       '';
     })
   ];
-
-  # XXX(2024/02/05): set GSK_RENDERER=cairo to solve graphical edge-case on moby where some JPEGs would render as black!
-  # - repro by loading komikku and viewing images. some fail (particularly mangadex onimai), some work.
-  # - run `GSK_RENDERER=help loupe` to see options.
-  # - TODO: see if i can enable the `vulkan` GSK_RENDERER?
-  # - for more on GSK_RENDERER: <https://blog.gtk.org/2024/01/28/new-renderers-for-gtk/>
-  # XXX(2024/02/21): GSK_RENDERER=cairo breaks `delfin`  (as does GSK_RENDERER=vulkan, when gtk4 is compiled with `vulkanSupport = true`)
-  # - perhaps it's best to let this be defaulted and set it ONLY where needed
-  # - upstream gtk recommends using mesa 24.0 (latest) specifically in response to the GSK renderers triggering new driver bugs,
-  #   so maybe i can update that before re-enabling GSK_RENDERER anywhere else.
-  # environment.variables.GSK_RENDERER = "cairo";
-
 }