Remove RTLD_GLOBAL hack for swig

[storborg]

If pyqt is imported prior to gr-qtgui being imported, usage of QwtPlot-based gr-qtgui widgets will fail at runtime with:

Object::connect: No such signal QwtPlotPicker::selected(const QPointF &)
Segmentation fault (core dumped)

This error is caused by the _RTLD_GLOBAL hack used by older versions of gr-modtool. The import order which exposes this problem may be generated by GRC in the specific circumstance of gr-pyqt being used inside a hierarchical block which has an ID that is alphabetically before gr-.

I haven't been able to find any reason to keep the hack around, and it isn't in most other current OOT modules. The specific platform I'm encountering the error on is GNU Radio v3.7.11 on Ubuntu 16.04.2 LTS, with up-to-date apt versions of Qt, PyQT4, etc.