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/src/feature.h b/src/feature.h
index d0bb78f..7e1e982 100644
--- a/src/feature.h
+++ b/src/feature.h
@@ -944,7 +944,7 @@
  *			Always included, since either FEAT_MOUSE_XTERM or
  *			DOS_MOUSE is defined.
  */
-// OS/2 and Amiga console have no mouse support
+// Amiga console has no mouse support
 #if defined(UNIX) || defined(VMS)
 # define FEAT_MOUSE_XTERM
 # ifdef FEAT_BIG