MXS-2612 Free routing worker local data

When a RoutingWorker is destructed, all existing local data will
unconditionally be destroyed.

The case in point is the vector<SFilterDef>s that are held as routing
worker local data by the Service. Unless the local data is deleted, the
filter defs will not be deleted at shutdown.

This is somewhat brute-force (but good to have in place nonetheless) as
the deletion of the local data should be done by the Service and before
the routing worker thread has exited.

server/core/routingworker.cc

@@ -267,6 +267,17 @@ RoutingWorker::RoutingWorker()
 
 RoutingWorker::~RoutingWorker()
 {
+    for (uint64_t key = 0; key < m_local_data.size(); ++key)
+    {
+        auto* pData = m_local_data[key];
+        auto deleter = m_data_deleters[key];
+
+        if (pData && deleter)
+        {
+            deleter(pData);
+        }
+    }
+
     delete m_pWatchdog_notifier;
 }