refactor(options)!: graduate some more shortmess flags

A lot of updated places in the docs were already incorrect since long
since they did not reflect the default behaviour.

"[dos format]" could've been argued being better for discoverability
but that ship has already sailed as it is no longer displayed by default.

src/nvim/options.lua

@@ -7239,22 +7239,17 @@ return {
     {
       abbreviation = 'shm',
       cb = 'did_set_shortmess',
-      defaults = { if_true = 'ilnxtToOCF' },
+      defaults = { if_true = 'ltToOCF' },
       desc = [=[
         This option helps to avoid all the |hit-enter| prompts caused by file
         messages, for example  with CTRL-G, and to avoid some other messages.
         It is a list of flags:
          flag	meaning when present	~
-          i	use "[noeol]" instead of "[Incomplete last line]"	*shm-i*
           l	use "999L, 888B" instead of "999 lines, 888 bytes"	*shm-l*
           m	use "[+]" instead of "[Modified]"			*shm-m*
-          n	use "[New]" instead of "[New File]"			*shm-n*
           r	use "[RO]" instead of "[readonly]"			*shm-r*
           w	use "[w]" instead of "written" for file write message	*shm-w*
         	and "[a]" instead of "appended" for ':w >> file' command
-          x	use "[dos]" instead of "[dos format]", "[unix]"		*shm-x*
-        	instead of "[unix format]" and "[mac]" instead of "[mac
-        	format]"
           a	all of the above abbreviations				*shm-a*
 
           o	overwrite message for writing a file with subsequent	*shm-o*