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/if_perl.txt b/runtime/doc/if_perl.txt
index db0a92c..7e33af2 100644
--- a/runtime/doc/if_perl.txt
+++ b/runtime/doc/if_perl.txt
@@ -1,4 +1,4 @@
-*if_perl.txt*   For Vim version 8.1.  Last change: 2019 Jan 29
+*if_perl.txt*   For Vim version 8.1.  Last change: 2019 May 05
 
 
 		  VIM REFERENCE MANUAL    by Sven Verdoolaege
@@ -11,9 +11,7 @@
 3. Using the Perl interface		|perl-using|
 4. Dynamic loading			|perl-dynamic|
 
-{Vi does not have any of these commands}
-
-The Perl interface only works when Vim was compiled with the |+perl| feature.
+{only available when Vim was compiled with the |+perl| feature}
 
 ==============================================================================
 1. Editing Perl files					*perl-editing*