Restructure Darwin configuration

So far, this is just based on mightymac. The other devices will be
updated soon.

modules/home-manager/files/nvim/lua/disabled/nvim-tree.lua

@@ -1,11 +0,0 @@
-return{
-  "nvim-tree/nvim-tree.lua",
-  config = function ()
-    vim.g.loaded_netrw = 1
-    vim.g.loaded_netrwPlugin = 1
-
-    require('nvim-tree').setup()
-
-    vim.keymap.set('n', '<c-n>', ':NvimTreeFindFileToggle<CR>')
-  end
-}