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/windows.txt b/runtime/doc/windows.txt
index 0b96115..9a682e5 100644
--- a/runtime/doc/windows.txt
+++ b/runtime/doc/windows.txt
@@ -1,4 +1,4 @@
-*windows.txt*   For Vim version 8.1.  Last change: 2019 Mar 17
+*windows.txt*   For Vim version 8.1.  Last change: 2019 May 05
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -26,7 +26,6 @@
 11. Using hidden buffers			|buffer-hidden|
 12. Special kinds of buffers			|special-buffers|
 
-{Vi does not have any of these commands}
 {not able to use multiple windows when the |+windows| feature was disabled at
 compile time}
 {not able to use vertically split windows when the |+vertsplit| feature was
@@ -737,7 +736,7 @@
 			the current window.
 			{cmd} can contain '|' to concatenate several commands.
 			{cmd} must not open or close windows or reorder them.
-			{not in Vi}
+
 			Also see |:tabdo|, |:argdo|, |:bufdo|, |:cdo|, |:ldo|,
 			|:cfdo| and |:lfdo|
 
@@ -765,7 +764,7 @@
 			autocommand event is disabled by adding it to
 			'eventignore'.  This considerably speeds up editing
 			each buffer.
-			{not in Vi}
+
 			Also see |:tabdo|, |:argdo|, |:windo|, |:cdo|, |:ldo|,
 			|:cfdo| and |:lfdo|
 
@@ -891,7 +890,7 @@
 							*:pp* *:ppop*
 :[count]pp[op][!]
 		Does ":[count]pop[!]" in the preview window.  See |:pop| and
-		|:ptag|.  {not in Vi}
+		|:ptag|.
 
 CTRL-W }						*CTRL-W_}*
 		Use identifier under cursor as a tag and perform a :ptag on