Prevent EntropyMixer from registering with service manager.

EntropyMixer is designed to be triggered in two ways, as either the
result of a self-set timer or of one of three system broadcasts.  It is not
meant to be triggered in any other way, so exposing it via servicemanager
is undesirable.

Bug: 18106000

Cherry-pick of commit: 9287e0dd272b85b475e33bcbd7d868517a0f98f9

Change-Id: I9aeb35e7ffde75090f4234ea193514fb883b1425
diff --git a/services/java/com/android/server/SystemServer.java b/services/java/com/android/server/SystemServer.java
index 8a64aa6..4d6a904 100644
--- a/services/java/com/android/server/SystemServer.java
+++ b/services/java/com/android/server/SystemServer.java
@@ -407,6 +407,7 @@
         ConsumerIrService consumerIr = null;
         AudioService audioService = null;
         MmsServiceBroker mmsService = null;
+        EntropyMixer entropyMixer = null;
 
         boolean disableStorage = SystemProperties.getBoolean("config.disable_storage", false);
         boolean disableMedia = SystemProperties.getBoolean("config.disable_media", false);
@@ -430,7 +431,7 @@
             ServiceManager.addService("telephony.registry", telephonyRegistry);
 
             Slog.i(TAG, "Entropy Mixer");
-            ServiceManager.addService("entropy", new EntropyMixer(context));
+            entropyMixer = new EntropyMixer(context);
 
             mContentResolver = context.getContentResolver();