refactor: move filetype customization from polish.lua to astrocore.lua (#31)

Co-authored-by: Mark Weng <mweng@nvidia.com>

lua/polish.lua

@@ -1,18 +1,5 @@
 if true then return end -- WARN: REMOVE THIS LINE TO ACTIVATE THIS FILE
 
--- This will run last in the setup process and is a good place to configure
--- things like custom filetypes. This is just pure lua so anything that doesn't
+-- This will run last in the setup process.
+-- This is just pure lua so anything that doesn't
 -- fit in the normal config locations above can go here
-
--- Set up custom filetypes
-vim.filetype.add {
-  extension = {
-    foo = "fooscript",
-  },
-  filename = {
-    ["Foofile"] = "fooscript",
-  },
-  pattern = {
-    ["~/%.config/foo/.*"] = "fooscript",
-  },
-}