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/sign.txt b/runtime/doc/sign.txt
index 4886f74..4f59c8f 100644
--- a/runtime/doc/sign.txt
+++ b/runtime/doc/sign.txt
@@ -1,4 +1,4 @@
-*sign.txt*      For Vim version 8.1.  Last change: 2019 Jan 17
+*sign.txt*      For Vim version 8.1.  Last change: 2019 May 05
 
 
 		  VIM REFERENCE MANUAL    by Gordon Prieur
@@ -10,7 +10,6 @@
 1. Introduction				|sign-intro|
 2. Commands				|sign-commands|
 
-{Vi does not have any of these features}
 {only available when compiled with the |+signs| feature}
 
 ==============================================================================