How do you undefine existing functions and key maps?

Question

I am looking at a scenario where in order to keep track of changes to my setup, rather than delete functions and keymaps defined in vimrc or other plugin I add commands which disable those functions and keymaps further down the execution sequence.

For example in the example below how would undo the mapping of the <cr> key and undefine the function like it was never created in the first place?

cnoremap <silent> <cr> <cr>:call <SID>CommandCallback()<cr>

function! s:CommandCallback()
  let last_command = @:

  if last_command =~ 'tabnew'
    echomsg "Tabnew was called"
  endif
endfunction

Answer 1

To remove a command-line mapping, use:

:cunmap {lhs}

Similar commands exist for the other mapping modes. See :help :unmap

To remove a function, use:

:delfunction {name}