Windows: Break dependency on OLE32

The OLE32 library provides the IIDFromString() function to parse a
string to a GUID, but we can implement a simple GUID parsing function
and remove this dependence. Doing so also avoids fetching the Unicode
form of the "DeviceInterfaceGUIDs" property.

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>