[functional tests] Remove dependency on the ThunderChez library.

I've just moved the relevant code into the functional-tests dir.

functional-tests/srfi/s6/basic-string-ports.sls

@@ -0,0 +1,20 @@
+;; Copyright (c) 2009 Derick Eddington.  All rights reserved.
+;; Licensed under an MIT-style license.  My license is in the file
+;; named LICENSE from the original collection this file is distributed
+;; with.  If this file is redistributed with some other collection, my
+;; license must also be included.
+
+#!r6rs
+(library (srfi s6 basic-string-ports)
+  (export
+    open-input-string
+    open-output-string
+    get-output-string)
+  (import
+    (rnrs base)
+    (only (rnrs io ports) open-string-input-port)
+    (srfi s6 basic-string-ports compat))
+  
+  (define (open-input-string str)
+    (open-string-input-port str))
+)