fix(mappings): remove un-indent mapping in favor of the default <C-D>

lua/core/mappings.lua

@@ -62,10 +62,10 @@ vim.keymap.set("", "<C-LeftMouse>", "")
 vim.cmd.aunmenu({ "PopUp.-1-", })
 vim.cmd.aunmenu({ "PopUp.How-to\\ disable\\ mouse", })
 
--- Shift+Tab to unindent
-vim.keymap.set("i", "<S-Tab>", function ()
-    local cursor = vim.api.nvim_win_get_cursor(0)
-    local row, col = cursor[1], cursor[2]
-    vim.cmd.normal("<<")
-    vim.api.nvim_win_set_cursor(0, { row, col - vim.o.shiftwidth, })
-end)
+-- Default bindings that are good to know:
+-- insert mode:
+--  <C-T>   -   indent, see :h i_CTRL-T
+--  <C-D>   -   un-indent, see :h i_CTRL-D
+-- normal mode:
+--  <count?><C-E>   -   scroll window down <count> lines, see :h CTRL-E
+--  <count?><C-Y>   -   scroll window up <count> lines, see :h CTRL-Y