Refactor: extract src/event_log.cpp

event_service_manager.hpp contains namespace 'event_log' which is
confusing. Extract it to a separate header and cpp file to have the
filename match the namespace.

No functional changes have been made to the code.

Tested:
- Using Redfish Event Listener, test subscriptions and eventing.
- Redfish Service Validator passes

Change-Id: Ia0bf658b8b46f92aede059d46e8de48f160e073e
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
Signed-off-by: Ed Tanous <ed@tanous.net>
diff --git a/redfish-core/src/subscription.cpp b/redfish-core/src/subscription.cpp
index f74435d..0b7a9fd 100644
--- a/redfish-core/src/subscription.cpp
+++ b/redfish-core/src/subscription.cpp
@@ -15,9 +15,9 @@
 */
 #include "subscription.hpp"
 
+#include "event_log.hpp"
 #include "event_logs_object_type.hpp"
 #include "event_matches_filter.hpp"
-#include "event_service_manager.hpp"
 #include "event_service_store.hpp"
 #include "filter_expr_executor.hpp"
 #include "generated/enums/log_entry.hpp"