Update ART tests to handle new System.gc behavior

Changed calls from System.gc to Runtime.getRuntime.gc where it was
necessary.

Required for:
https://android-review.googlesource.com/#/c/80253/

Change-Id: I2b0622585da54229a6248e95d40134b6d18598a9
diff --git a/test/030-bad-finalizer/src/Main.java b/test/030-bad-finalizer/src/Main.java
index e19fd3e..330e344 100644
--- a/test/030-bad-finalizer/src/Main.java
+++ b/test/030-bad-finalizer/src/Main.java
@@ -25,12 +25,12 @@
         bf = null;
 
         System.out.println("Nulled. Requestion gc.");
-        System.gc();
+        Runtime.getRuntime().gc();
 
         for (int i = 0; i < 8; i++) {
             BadFinalizer.snooze(4000);
             System.out.println("Requesting another GC.");
-            System.gc();
+            Runtime.getRuntime().gc();
         }
 
         System.out.println("Done waiting.");