refactor: remove unused setup function

Colorschemes load via :colorscheme command, making the setup() no-op redundant.

lua/midnight/init.lua

@@ -1,14 +1,5 @@
 local M = {}
 
----@class MidnightConfig
----@field [string] any
-
----@param opts? MidnightConfig
----@return nil
-function M.setup(opts)
-  opts = opts or {}
-end
-
 ---@return nil
 function M.load()
   if vim.g.colors_name then