health: do not use default destructor.

Otherwise, clients will need to know how to destroy
LinkedCallback, a hidden class.

Test: builds
Bug: 177269435
Change-Id: I89532755da16b672c4cbece55b943306f68cdb9e
diff --git a/health/aidl/default/Health.cpp b/health/aidl/default/Health.cpp
index 812e64a..e1d1982 100644
--- a/health/aidl/default/Health.cpp
+++ b/health/aidl/default/Health.cpp
@@ -60,6 +60,8 @@
     battery_monitor_.init(healthd_config_.get());
 }
 
+Health::~Health() {}
+
 //
 // Getters.
 //