Remove apex-pdp unused core modules

This is the final review in the refactoring of the model code in
apex-pdp.

The core-messaging and core-infrastructure modules are unused in
apex-pdp except for websocket communication. Websocket communication is
also not used in any deployment.

This review:
- removes the core-mesaging module, which had an apex-specific websocket
  implementation, except for the MessageException class, which is moved
  to the base core module
- removes the core-infrastructure module, except for the ThreadUtils
  class, which is moved to the base core module
- removes the websocket event protocol, which used core-messaging but is
  not used in any deployment
- collapses all three "core" submodules into a single module
- Updates dependencies where needed

Issue-ID: POLICY-1820
Change-Id: Ieae30063e99570e61943372d3fa23b77a211462c
Signed-off-by: liamfallon <liam.fallon@est.tech>
diff --git a/examples/examples-aadm/pom.xml b/examples/examples-aadm/pom.xml
index 5e8ba05..9d7fff4 100644
--- a/examples/examples-aadm/pom.xml
+++ b/examples/examples-aadm/pom.xml
@@ -1,6 +1,7 @@
 <!--
   ============LICENSE_START=======================================================
    Copyright (C) 2018 Ericsson. All rights reserved.
+   Modifications Copyright (C) 2022 Nordix Foundation.
   ================================================================================
   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
@@ -37,13 +38,7 @@
         </dependency>
         <dependency>
             <groupId>org.onap.policy.apex-pdp.core</groupId>
-            <artifactId>core-engine</artifactId>
-            <version>${project.version}</version>
-            <scope>test</scope>
-        </dependency>
-        <dependency>
-            <groupId>org.onap.policy.apex-pdp.core</groupId>
-            <artifactId>core-infrastructure</artifactId>
+            <artifactId>core</artifactId>
             <version>${project.version}</version>
             <scope>test</scope>
         </dependency>