SystemServer: only enable fd leak tracker on eng

Change-Id: Ic85d351558dea5a5446c5ebe468b0db9e8c99285

services/java/com/android/server/SystemServer.java

@@ -879,7 +879,7 @@ public final class SystemServer implements Dumpable {
             initZygoteChildHeapProfiling();
 
             // Debug builds - spawn a thread to monitor for fd leaks.
-            if (Build.IS_DEBUGGABLE) {
+            if (Build.IS_ENG) {
                 spawnFdLeakCheckThread();
             }