patch 8.2.0017: OS/2 and MS-DOS are still mentioned

Problem:    OS/2 and MS-DOS are still mentioned, even though support was
            removed long ago.
Solution:   Update documentation. (Yegappan Lakshmanan, closes #5368)
diff --git a/runtime/doc/autocmd.txt b/runtime/doc/autocmd.txt
index 3588756..e2e9567 100644
--- a/runtime/doc/autocmd.txt
+++ b/runtime/doc/autocmd.txt
@@ -1,4 +1,4 @@
-*autocmd.txt*   For Vim version 8.2.  Last change: 2019 Dec 11
+*autocmd.txt*   For Vim version 8.2.  Last change: 2019 Dec 17
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1289,8 +1289,8 @@
 	[^ch]   match any character but 'c' and 'h'
 
 Note that for all systems the '/' character is used for path separator (even
-MS-DOS and OS/2).  This was done because the backslash is difficult to use
-in a pattern and to make the autocommands portable across different systems.
+for MS-Windows).  This was done because the backslash is difficult to use in a
+pattern and to make the autocommands portable across different systems.
 
 It is possible to use |pattern| items, but they may not work as expected,
 because of the translation done for the above.