vout: win32: Remove an unused local property key definition

This one used to be missing from mingw-w64 headers, but was added there
yesterday in git master.

If this one actually is used, and we can't be sure of whether it exists
in system headers, we could define it ourselves, but with a unique
prefix. But in this case it simply seems to be unused.

This fixes compilation with the very latest mingw-w64 headers.

modules/video_output/win32/sensors.cpp

@@ -35,10 +35,6 @@
 
 #include <new>
 
-#ifndef _MSC_VER
-DEFINE_PROPERTYKEY(SENSOR_DATA_TYPE_MAGNETOMETER_ACCURACY, 0x1637d8a2, 0x4248, 0x4275, 0x86, 0x5d, 0x55, 0x8d, 0xe8, 0x4a, 0xed, 0xfd, 22);
-#endif
-
 class SensorReceiver : public ISensorEvents
 {
 public: