fix: remove default browser

i dont use qutebrowser anymore

lua/custom/plugins/md.lua

@@ -3,7 +3,4 @@ return {
   cmd = { "MarkdownPreviewToggle", "MarkdownPreview", "MarkdownPreviewStop" },
   ft = { "markdown" },
   build = function() vim.fn["mkdp#util#install"]() end,
-  config = function()
-    vim.g.mkdp_browser = '/usr/bin/qutebrowser'
-  end
 }