IDL: Drop value conversion (V8 -> C++) macros from generated code

Source/bindings/templates/conversions.cpp

+{% macro v8_value_to_local_cpp_value(thing) %}
+{# This indirection is just to avoid spurious white-space lines. #}
+{{generate_v8_value_to_local_cpp_value(thing) | trim}}
+{%- endmacro %}
+
+
+{% macro generate_v8_value_to_local_cpp_value(thing) %}
+{% set item = thing.v8_value_to_local_cpp_value or thing %}
+{% if item.error_message %}
+/* {{item.error_message}} */
+{% else %}
+{% if item.declare_variable %}
+{% if item.assign_expression %}
+{{item.cpp_type}} {{item.cpp_name}} = {{item.assign_expression}};
+{% else %}
+{{item.cpp_type}} {{item.cpp_name}};
+{% endif %}
+{% else %}{# item.declare_variable #}
+{% if item.assign_expression %}
+{{item.cpp_name}} = {{item.assign_expression}};
+{% endif %}
+{% endif %}{# item.declare_variable #}
+{% if item.set_expression %}
+{{item.set_expression}};
+{% endif %}
+{% if item.check_expression %}
+if ({{item.check_expression}})
+    return{% if item.return_expression %} {{item.return_expression}}{% endif %};
+{% endif %}{# item.check_expression #}
+{% endif %}{# item.error_message #}
+{% endmacro %}