Fix Collections import. (#2715)

Author: vkryachko

transport/transport-runtime/src/test/java/com/google/android/datatransport/runtime/scheduling/jobscheduling/ScheduleDelayTest.java

@@ -19,7 +19,7 @@
 import com.google.android.datatransport.Priority;
 import com.google.android.datatransport.runtime.time.Clock;
 import com.google.android.datatransport.runtime.time.TestClock;
-import edu.emory.mathcs.backport.java.util.Collections;
+import java.util.Collections;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.robolectric.RobolectricTestRunner;