runtime(doc): update documentation on tabstop settings

Unify the treatment of tabstop, correct errors and deprecate smarttab
usage.

closes: #17444

Signed-off-by: Damien Lejay <damien@lejay.be>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/usr_30.txt b/runtime/doc/usr_30.txt
index 86fe649..59ef37a 100644
--- a/runtime/doc/usr_30.txt
+++ b/runtime/doc/usr_30.txt
@@ -1,4 +1,4 @@
-*usr_30.txt*	For Vim version 9.1.  Last change: 2025 May 30
+*usr_30.txt*	For Vim version 9.1.  Last change: 2025 Jun 10
 
 		     VIM USER MANUAL - by Bram Moolenaar
 
@@ -547,8 +547,8 @@
 
   If you prefer to have different values for 'shiftwidth' and 'softtabstop',
 you can still do so and use <C-t> to indent with 'shiftwidth'.  Or you can
-use the 'smarttab' option introduced in Vim 5.6, allowing for a unified
-<Tab> key that knows what to do in the different situations.
+use the 'smarttab' option, allowing for a unified <Tab> key that knows what to
+do in the different situations.
 
 
 VARIABLE TAB STOPS