Cleanup after #3007 #3020

'guioptions' is mentioned in the "Option Defaults" section of vim_diff,
and while its default did indeed change, it was only because the 't'
flag was removed.  To make that clear, move its reference to the
"Removed Features" section instead.

Remove stray instance of 't' flag from GO_ALL.  Most if not all of the
GO_* #defines are unused, but lets keep them for now as it's not clear
whether they won't be used by Nvim GUIs.

runtime/doc/vim_diff.txt

@@ -35,7 +35,6 @@ these differences.
 - 'display' defaults to "lastline"
 - 'encoding' defaults to "utf-8"
 - 'formatoptions' defaults to "tcqj"
-- 'guioptions' doesn't include "t"
 - 'hlsearch' is set by default
 - 'incsearch' is set by default
 - 'langnoremap' is set by default
@@ -136,6 +135,7 @@ Highlight groups:
   |hl-VisualNOS|
 
 Other options:
+  'guioptions' (only the 't' flag was removed)
   'guipty'
   'macatsui'
   'shelltype'

src/nvim/option_defs.h

@@ -203,7 +203,7 @@
 #define GO_TOOLBAR      'T'             /* add toolbar */
 #define GO_FOOTER       'F'             /* add footer */
 #define GO_VERTICAL     'v'             /* arrange dialog buttons vertically */
-#define GO_ALL          "aAbcefFghilmMprtTv" /* all possible flags for 'go' */
+#define GO_ALL          "aAbcefFghilmMprTv" /* all possible flags for 'go' */
 
 /* flags for 'comments' option */
 #define COM_NEST        'n'             /* comments strings nest */