doc: mark macatsui option as removed, update vim_diff.txt

This option has already been removed in the source.

Nvim does not have a GUI, so `nvim -g` does not work.
Also add `macatsui` to the list of removed options.

runtime/doc/vim_diff.txt

@@ -110,6 +110,7 @@ MS-DOS support:
   'conskey'
 
 Other options:
+  'macatsui'
   'shortname'
   'shelltype'
   'textauto'
@@ -123,6 +124,9 @@ Other commands:
 Other compile-time features:
   EBCDIC
 
+Nvim does not have a built-in GUI and hence the following aliases have been
+removed: gvim, gex, gview, rgvim, rgview
+
 "Easy mode" (eview, evim, nvim -y)
 "(g)vimdiff" (alias for "(g)nvim -d" |diff-mode|)
 "Vi mode" (nvim -v)
@@ -133,13 +137,8 @@ of just using their command line arguments:
   ex        nvim -e
   exim      nvim -E
   view      nvim -R
-  gvim      nvim -g
-  gex       nvim -eg
-  gview     nvim -Rg
   rvim      nvim -Z
   rview     nvim -RZ
-  rgvim     nvim -gZ
-  rgview    nvim -RgZ
 
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