Remove unnecessary includes from Optional.h

Summary:
I want to be able to include this in
fbobjc/xplat/folly:headers_only, but it currently pulls in a boost
header and Portability.h. Fortunately, neither of those includes are
needed.

Reviewed By: ddrcoder, yfeldblum, mhorowitz

Differential Revision: D2880443

fb-gh-sync-id: 409561b8fb555ac3946d59cd6657c6c643b67c86

folly/Optional.h

@@ -59,10 +59,6 @@
 #include <type_traits>
 #include <utility>
 
-#include <boost/operators.hpp>
-
-#include <folly/Portability.h>
-
 namespace folly {
 
 namespace detail { struct NoneHelper {}; }

folly/test/OptionalTest.cpp

@@ -15,6 +15,7 @@
  */
 
 #include <folly/Optional.h>
+#include <folly/Portability.h>
 
 #include <memory>
 #include <vector>