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/insert.txt b/runtime/doc/insert.txt
index 8ba360b..87407e1 100644
--- a/runtime/doc/insert.txt
+++ b/runtime/doc/insert.txt
@@ -300,8 +300,7 @@
 
 						*i_CTRL-X* *insert_expand*
 CTRL-X enters a sub-mode where several commands can be used.  Most of these
-commands do keyword completion; see |ins-completion|.  These are not available
-when Vim was compiled without the |+insert_expand| feature.
+commands do keyword completion; see |ins-completion|.
 
 Two commands can be used to scroll the window up or down, without exiting
 insert mode:
@@ -609,9 +608,6 @@
 keyword or line that has been typed.  This is useful if you are using
 complicated keywords (e.g., function names with capitals and underscores).
 
-These commands are not available when the |+insert_expand| feature was
-disabled at compile time.
-
 Completion can be done for:
 
 1. Whole lines						|i_CTRL-X_CTRL-L|