Allow removal of properties via typesystem XML

Not every property defined on a C++ class is necessarily meant to be included in the bindings generated by Shiboken, as they may allow access to features that are either internal to the project or are for other reasons considered not to be fit to be used from the Python side.

Shiboken provides the facilities to add new properties to an existing class in the typesystem XML file by use of the property tag, but this feature does not allow to specify the exclusion of an existing property from the generated headers.

As such, a feature that allows the user to specify via the typesystem XML file to have these properties removed from the generated bindings would be welcome.