hidl-gen: use Return<void>

C++ HIDL methods now return Return<> objects regadless of elision
status.  This hides Status from auto-generated code.

b/31367910
b/31348667
b/31365311

Change-Id: Ib009d2bade022a557f51d3cd4cb3e61ece38bba2
Signed-off-by: Iliyan Malchev <malchev@google.com>
diff --git a/Method.cpp b/Method.cpp
index 230ba17..8b592fd 100644
--- a/Method.cpp
+++ b/Method.cpp
@@ -58,7 +58,7 @@
     const TypedVar *elidedReturn = canElideCallback();
 
     if (elidedReturn == nullptr) {
-        out << "::android::hardware::Status ";
+        out << "::android::hardware::Return<void> ";
     } else {
         std::string extra;
         out << "::android::hardware::Return<"