Modifiable: No virtual destructor

There's only three classes that inherit from Modifiable today. The
virtual destructor adds an extra 8 byte vtable to every instance of
table, record or vector values.
Calling Unregister() explicitly from the destructors explicitly saves
8 bytes of memory for each instance.

src/Notifier.cc

@@ -62,9 +62,4 @@ void Registry::Terminate() {
     }
 }
 
-Modifiable::~Modifiable() {
-    if ( num_receivers )
-        registry.Unregister(this);
-}
-
 } // namespace zeek::notifier::detail

src/Notifier.h

@@ -99,8 +99,6 @@ extern Registry registry;
  */
 class Modifiable {
 public:
-    virtual ~Modifiable();
-
     /**
      * Calling this method signals to all registered receivers that the
      * object has been modified.
@@ -110,6 +108,17 @@ public:
             registry.Modified(this);
     }
 
+    /**
+     * Unregister this instance from the registry.
+     *
+     * Classes inheriting from Modifiable are required to call
+     * this from the destructor explicitly.
+     */
+    void Unregister() {
+        if ( num_receivers )
+            registry.Unregister(this);
+    }
+
 protected:
     friend class Registry;
 

src/Val.cc

@@ -31,6 +31,7 @@
 #include "zeek/IPAddr.h"
 #include "zeek/IntrusivePtr.h"
 #include "zeek/NetVar.h"
+#include "zeek/Notifier.h"
 #include "zeek/Overflow.h"
 #include "zeek/PrefixTable.h"
 #include "zeek/RE.h"
@@ -1712,6 +1713,8 @@ void TableVal::Init(TableTypePtr t, bool ordered) {
 }
 
 TableVal::~TableVal() {
+    notifier::detail::Modifiable::Unregister();
+
     if ( timer )
         detail::timer_mgr->Cancel(timer);
 
@@ -2952,6 +2955,8 @@ RecordVal::RecordVal(RecordTypePtr t, std::vector<std::optional<ZVal>> init_vals
 }
 
 RecordVal::~RecordVal() {
+    notifier::detail::Modifiable::Unregister();
+
     auto n = record_val.size();
 
     for ( unsigned int i = 0; i < n; ++i ) {
@@ -3234,6 +3239,8 @@ VectorVal::VectorVal(VectorTypePtr t, std::vector<std::optional<ZVal>>* vals) :
 }
 
 VectorVal::~VectorVal() {
+    notifier::detail::Modifiable::Unregister();
+
     if ( yield_types ) {
         int n = yield_types->size();
         for ( auto i = 0; i < n; ++i ) {