Remove unused core-system-modules

Soong tests no longer need to define a dummy version of this.

Test: m checkbuild
Bug: 141613583
Change-Id: Iad12560aedc74a499808bd52d9ea09ab0d68d743
diff --git a/java/testing.go b/java/testing.go
index 5315b85..acbefb9 100644
--- a/java/testing.go
+++ b/java/testing.go
@@ -103,7 +103,6 @@
 	`
 
 	systemModules := []string{
-		"core-system-modules",
 		"core-current-stubs-system-modules",
 		"core-platform-api-stubs-system-modules",
 		"android_stubs_current_system_modules",