Add explicit dep on services.backup

android_robolectric_test is having some implicit deps removed
from it, so add in what we depend on directly.

Test: m RunFrameworksServicesRoboTests
Change-Id: Ice2abeb3f4d031cfe15ce919b750d6de59316c1f

services/robotests/Android.bp

@@ -43,6 +43,7 @@ android_robolectric_test {
     // Include the testing libraries
     libs: [
         "platform-test-annotations",
+        "services.backup",
         "testng",
     ],
     static_libs: [