vim:coc: Re-enable backup files

CoC disables backup files due to a problem with a typescript
language-server (it becoming slow when the backup file is written,
triggering a `structureChanged`). But:

1. I want backup files
2. I do not use that language server
3. If I would:
	1. I could disable backup files in a filetype plugin
	2. The linked issue is from 2019 - no idea if this is still
	   present today
4. I don't think this issue is even a thing with a `&backupdir` that
   does not include relative directories (which is the case for me)

So remove the lines disabling backups and go back to vim's defaults:
`nobackup` and `writebackup`.

Link: https://github.com/neoclide/coc.nvim/issues/649

.config/vim/vimrc.d/25-coc.vim

@@ -6,10 +6,6 @@ if !exists('g:did_coc_loaded')
 	finish
 endif
 
-" Some servers have issues with backup files, see #649.
-set nobackup
-set nowritebackup
-
 " Always show the signcolumn, otherwise it would shift the text each time
 " diagnostics appear/become resolved.
 set signcolumn=yes