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/tools/README.txt b/runtime/tools/README.txt
index fa176c7..19976b3 100644
--- a/runtime/tools/README.txt
+++ b/runtime/tools/README.txt
@@ -34,4 +34,4 @@
 
 unicode.vim	Vim script to generate tables for src/mbyte.c.
 
-[xxd (and tee for OS/2) can be found in the src directory]
+[xxd can be found in the src directory]