Review DLLs bundled by `pyqt-bundle`

[philthompson10]

Currently pyqt-bundle bundles DLLs for OpenSSL, the C++ runtime and the C runtime. These should be reviewed to see if they are all still required. The following points need to be taken into account...

• Qt5 still needs to be supported
• all supported versions of Python include the C runtime (but are they accessible by the Qt DLLs?)
• the recommendation for C++ extension modules is that they dynamically link the C runtime and statically link the C++ runtime (however it's not clear how to do this, and the Qt DLLs probably dynamically link the C++ runtime anyway).