interrogate: remove Dtool_AddToDictionary (let me know if anyone uses this)

If any code is relying on this, please let me know and I will add it back.  It appears to be redundant, though, since one can access DtoolClassDict directly.

Symbol kept around temporarily in order to keep ABI compatibility for a short while as people may not update their interrogate and Panda in sync, but it can soon be removed.

dtool/src/interrogate/interfaceMakerPythonNative.cxx

@@ -1459,7 +1459,7 @@ write_module_support(ostream &out, ostream *out_h, InterrogateModuleDef *def) {
   if (force_base_functions) {
     out << "  // Support Function For Dtool_types ... for now in each module ??\n";
     out << "  {\"Dtool_BorrowThisReference\", &Dtool_BorrowThisReference, METH_VARARGS, \"Used to borrow 'this' pointer (to, from)\\nAssumes no ownership.\"},\n";
-    out << "  {\"Dtool_AddToDictionary\", &Dtool_AddToDictionary, METH_VARARGS, \"Used to add items into a tp_dict\"},\n";
+    //out << "  {\"Dtool_AddToDictionary\", &Dtool_AddToDictionary, METH_VARARGS, \"Used to add items into a tp_dict\"},\n";
   }
 
   out << "  {nullptr, nullptr, 0, nullptr}\n" << "};\n\n";

dtool/src/interrogatedb/py_panda.cxx

@@ -704,7 +704,7 @@ PyObject *Dtool_BorrowThisReference(PyObject *self, PyObject *args) {
 
 // We do expose a dictionay for dtool classes .. this should be removed at
 // some point..
-PyObject *Dtool_AddToDictionary(PyObject *self1, PyObject *args) {
+EXPCL_INTERROGATEDB PyObject *Dtool_AddToDictionary(PyObject *self1, PyObject *args) {
   PyObject *self;
   PyObject *subject;
   PyObject *key;

dtool/src/interrogatedb/py_panda.h

@@ -329,10 +329,6 @@ EXPCL_INTERROGATEDB PyObject *Dtool_PyModuleInitHelper(LibraryDef *defs[], const
 // historical inharatence in the for of "is this instance of"..
 EXPCL_INTERROGATEDB PyObject *Dtool_BorrowThisReference(PyObject *self, PyObject *args);
 
-// We do expose a dictionay for dtool classes .. this should be removed at
-// some point..
-EXPCL_INTERROGATEDB PyObject *Dtool_AddToDictionary(PyObject *self1, PyObject *args);
-
 #define DTOOL_PyObject_HashPointer DtoolInstance_HashPointer
 #define DTOOL_PyObject_ComparePointers DtoolInstance_ComparePointers