Add method to remove test from tracked loopers

Add method to remove a test from the sLoopers map, since keeping them
around forever results in a memory leak for large test suites.

Bug: 156287358
Test: atest FrameworksTelephonyTests
Change-Id: I553ea3a1dac3ff4107e0c7caabee26d21f4c52f8

tests/testables/src/android/testing/TestableLooper.java

@@ -222,6 +222,10 @@ public class TestableLooper {
         return sLoopers.get(test);
     }
 
+    public static void remove(Object test) {
+        sLoopers.remove(test);
+    }
+
     static class LooperFrameworkMethod extends FrameworkMethod {
         private HandlerThread mHandlerThread;