patch 8.1.1901: the +insert_expand feature is not always available

Problem:    The +insert_expand feature is not always available.
Solution:   Graduate the +insert_expand feature.
diff --git a/runtime/doc/index.txt b/runtime/doc/index.txt
index f6cf2b5..091ffb2 100644
--- a/runtime/doc/index.txt
+++ b/runtime/doc/index.txt
@@ -1,4 +1,4 @@
-*index.txt*     For Vim version 8.1.  Last change: 2019 Aug 16
+*index.txt*     For Vim version 8.1.  Last change: 2019 Aug 21
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -166,7 +166,6 @@
 |i_CTRL-X_CTRL-V|	CTRL-X CTRL-V	complete like in : command line
 |i_CTRL-X_CTRL-]|	CTRL-X CTRL-]	complete tags
 |i_CTRL-X_s|		CTRL-X s	spelling suggestions
-{not available when compiled without the |+insert_expand| feature}
 
 commands in completion mode (see |popupmenu-keys|)