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/digraph.txt b/runtime/doc/digraph.txt
index a174d3c..b87dc0d 100644
--- a/runtime/doc/digraph.txt
+++ b/runtime/doc/digraph.txt
@@ -1,4 +1,4 @@
-*digraph.txt*   For Vim version 8.1.  Last change: 2019 Feb 17
+*digraph.txt*   For Vim version 8.1.  Last change: 2019 May 05
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -18,7 +18,6 @@
 2. Using digraphs	|digraphs-use|
 3. Default digraphs	|digraphs-default|
 
-{Vi does not have any of these commands}
 
 ==============================================================================
 1. Defining digraphs					*digraphs-define*