Don't store a static instance of UserManager

Otherwise the context within it can't be GCed.
It's better to leave the caching to the ContextImpl.

Bug: 25308506
Change-Id: I9be3ba5b1bb6cdc88b77520b2fbd72d9b72ef30d
diff --git a/core/java/android/os/UserManager.java b/core/java/android/os/UserManager.java
index 1c1575e..bc49b23 100644
--- a/core/java/android/os/UserManager.java
+++ b/core/java/android/os/UserManager.java
@@ -499,14 +499,9 @@
     /** @hide */
     public static final int PIN_VERIFICATION_SUCCESS = -1;
 
-    private static UserManager sInstance = null;
-
     /** @hide */
-    public synchronized static UserManager get(Context context) {
-        if (sInstance == null) {
-            sInstance = (UserManager) context.getSystemService(Context.USER_SERVICE);
-        }
-        return sInstance;
+    public static UserManager get(Context context) {
+        return (UserManager) context.getSystemService(Context.USER_SERVICE);
     }
 
     /** @hide */