replace dashboard with alpha.nvim (#816)

lua/core/mappings.lua

@@ -140,16 +140,6 @@ M.comment = function()
    map("v", m, ":lua require('Comment.api').toggle_linewise_op(vim.fn.visualmode())<CR>")
 end
 
-M.dashboard = function()
-   local m = plugin_maps.dashboard
-
-   map("n", m.bookmarks, ":DashboardJumpMarks <CR>")
-   map("n", m.new_file, ":DashboardNewFile <CR>")
-   map("n", m.open, ":Dashboard <CR>")
-   map("n", m.session_load, ":SessionLoad <CR>")
-   map("n", m.session_save, ":SessionSave <CR>")
-end
-
 M.lspconfig = function()
    local m = plugin_maps.lspconfig