fix(doc): :sleep! does not hide cursor

:sleep is the same as :sleep! in the port of v8.2.2366

runtime/doc/index.txt

@@ -1547,8 +1547,6 @@ tag		command		action ~
 |:sign|		:sig[n]		manipulate signs
 |:silent|	:sil[ent]	run a command silently
 |:sleep|	:sl[eep]	do nothing for a few seconds
-|:sleep!|	:sl[eep]!	do nothing for a few seconds, without the
-				cursor visible
 |:slast|	:sla[st]	split window and go to last file in the
 				argument list
 |:smagic|	:sm[agic]	:substitute with 'magic'

runtime/doc/various.txt

@@ -506,7 +506,8 @@ gO			Show a filetype-specific, navigable "outline" of the
 			Queued messages are processed during the sleep.
 
 							*:sl!* *:sleep!*
-:[N]sl[eep]! [N] [m]	Same as above, but hide the cursor.
+:[N]sl[eep]! [N] [m]	Same as above. Unlike Vim, it does not hide the
+			cursor. |vim-differences|
 
 ==============================================================================
 2. Using Vim like less or more					*less*

runtime/doc/vim_diff.txt

@@ -424,6 +424,7 @@ Commands:
   :promptfind
   :promptrepl
   :shell
+  :sleep! (does not hide the cursor; same as :sleep)
   :smile
   :tearoff