Remove unnecessary std::move from test_dex_file_builder

This stops Clang from warning about -Wpessimizing-move.

Change-Id: Id40acf1c398c615faf6486ef700df6975a5f013f
diff --git a/compiler/utils/test_dex_file_builder.h b/compiler/utils/test_dex_file_builder.h
index b1d7b4c..b6a228c 100644
--- a/compiler/utils/test_dex_file_builder.h
+++ b/compiler/utils/test_dex_file_builder.h
@@ -216,7 +216,7 @@
     std::unique_ptr<const DexFile> dex_file(DexFile::Open(
         &dex_file_data_[0], dex_file_data_.size(), dex_location, 0u, nullptr, &error_msg));
     CHECK(dex_file != nullptr) << error_msg;
-    return std::move(dex_file);
+    return dex_file;
   }
 
   uint32_t GetStringIdx(const std::string& type) {