libbinder: Remove templated binder::Status stream operator.

The templated binder::Status stream operator doesn't work with gmock
because of ambiguous operator overloading. Limiting the stream operator
to just std::stringstream allows it to be used with gmock.

BUG=28171901
TEST=Compiles with gmock and CameraBinderTests

Change-Id: Ia674b68cbff4911b3f5cc3d8ee57d04a1d6cf6bf
diff --git a/libs/binder/Status.cpp b/libs/binder/Status.cpp
index d3520d6..5ae6db2 100644
--- a/libs/binder/Status.cpp
+++ b/libs/binder/Status.cpp
@@ -158,5 +158,10 @@
     return ret;
 }
 
+std::stringstream& operator<< (std::stringstream& stream, const Status& s) {
+    stream << s.toString8().string();
+    return stream;
+}
+
 }  // namespace binder
 }  // namespace android