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/channel.txt b/runtime/doc/channel.txt
index cb6f781..ea0274f 100644
--- a/runtime/doc/channel.txt
+++ b/runtime/doc/channel.txt
@@ -1,4 +1,4 @@
-*channel.txt*      For Vim version 8.1.  Last change: 2019 Mar 21
+*channel.txt*      For Vim version 8.1.  Last change: 2019 May 05
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -24,7 +24,6 @@
 11. Controlling a job			|job-control|
 12. Using a prompt buffer		|prompt-buffer|
 
-{Vi does not have any of these features}
 {only when compiled with the |+channel| feature for channel stuff}
 	You can check this with: `has('channel')`
 {only when compiled with the |+job| feature for job stuff}