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/eval.txt b/runtime/doc/eval.txt
index b28fac9..eeb19e9 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -9753,7 +9753,7 @@
 		The command executed is constructed using several options:
 	'shell' 'shellcmdflag' 'shellxquote' {expr} 'shellredir' {tmp} 'shellxquote'
 		({tmp} is an automatically generated file name).
-		For Unix and OS/2 braces are put around {expr} to allow for
+		For Unix, braces are put around {expr} to allow for
 		concatenated commands.
 
 		The command will be executed in "cooked" mode, so that a