[Bindings][Refactoring] Move logics of preparePrototypeAndInterfaceObject from .tmpl to .py

third_party/WebKit/Source/bindings/templates/partial_interface.cpp.tmpl

 {% extends 'interface_base.cpp.tmpl' %}
 
-{% set has_prepare_prototype_and_interface_object =
-    unscopables or has_conditional_attributes_on_prototype or
-    methods | conditionally_exposed(is_partial) %}
-{% set prepare_prototype_and_interface_object_func =
-    '%s::preparePrototypeAndInterfaceObject' % v8_class_or_partial
-    if has_prepare_prototype_and_interface_object
-    else 'nullptr' %}
-
-
 {##############################################################################}
 {% block partial_interface %}
 void {{v8_class_or_partial}}::initialize() {
   // Should be invoked from ModulesInitializer.
   {{v8_class}}::updateWrapperTypeInfo(
       &{{v8_class_or_partial}}::install{{v8_class}}Template,
       {% if needs_runtime_enabled_installer %}
       &{{v8_class_or_partial}}::installRuntimeEnabledFeatures,
       {% else %}
       nullptr,
       {% endif %}
-      {{prepare_prototype_and_interface_object_func}});
+      {{prepare_prototype_and_interface_object_func or 'nullptr'}});
   {% for method in methods %}
   {% if method.overloads and method.overloads.has_partial_overloads %}
   {{v8_class}}::register{{method.name | blink_capitalize}}MethodForPartialInterface(&{{cpp_class_or_partial}}V8Internal::{{method.name}}Method);
   {% endif %}
   {% endfor %}
 }
 
 {% endblock %}