stringio.c: remove unnecessary check

* ext/stringio/stringio.c (writable): remove unnecessary check for
  deprecated safe level 4.  [Fix GH-963]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51207 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Fri Jul 10 10:46:02 2015  ksss  <co000ri@gmail.com>
+
+	* ext/stringio/stringio.c (writable): remove unnecessary check for
+	  deprecated safe level 4.  [Fix GH-963]
+
 Thu Jul  9 15:07:12 2015  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* win32/win32.c (waitpid): return immediately if interrupted.

ext/stringio/stringio.c

@@ -139,8 +139,6 @@ writable(VALUE strio)
     if (!WRITABLE(strio)) {
 	rb_raise(rb_eIOError, "not opened for writing");
     }
-    if (!OBJ_TAINTED(ptr->string)) {
-    }
     return ptr;
 }