patch 8.1.1280: remarks about functionality not in Vi clutters the help

Problem:    Remarks about functionality not in Vi clutters the help.
Solution:   Move all info about what is new in Vim or already existed in Vi to
            vi_diff.txt.  Remove {not in Vi} remarks. (closes #4268) Add
            "noet" to the help files modeline.  Also include many other help
            file improvements.
diff --git a/runtime/doc/gui.txt b/runtime/doc/gui.txt
index 2a8a70d..c24d672 100644
--- a/runtime/doc/gui.txt
+++ b/runtime/doc/gui.txt
@@ -1,4 +1,4 @@
-*gui.txt*       For Vim version 8.1.  Last change: 2019 Apr 28
+*gui.txt*       For Vim version 8.1.  Last change: 2019 May 05
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -19,7 +19,6 @@
 |gui_x11.txt|	For specific items of the X11 GUI.
 |gui_w32.txt|	For specific items of the Win32 GUI.
 
-{Vi does not have any of these commands}
 
 ==============================================================================
 1. Starting the GUI				*gui-start* *E229* *E233*