Fix ONOS CI by removing the usage of getRegisteredApps

getRegisteredApps is deprecated and it has been discontinued

This patch partially reverts:
- https://gerrit.onosproject.org/c/onos/+/22325
- https://gerrit.onosproject.org/c/onos/+/22362
- https://gerrit.onosproject.org/c/onos/+/22382

Change-Id: I652d814a006709bd40a673699697ba229955b0e4
diff --git a/core/api/src/main/java/org/onosproject/app/ApplicationService.java b/core/api/src/main/java/org/onosproject/app/ApplicationService.java
index 0f2d155..aa6b8e6 100644
--- a/core/api/src/main/java/org/onosproject/app/ApplicationService.java
+++ b/core/api/src/main/java/org/onosproject/app/ApplicationService.java
@@ -91,7 +91,10 @@
      * Returns the set of all installed applications.
      *
      * @return set of apps putside the build/core environment
+     *
+     * @deprecated since onos-2.5
      */
+    @Deprecated
     default Set<Application> getRegisteredApplications() {
         return ImmutableSet.of();
     }