Revert "Use a single libusb context"

This reverts commit c8a6dc6c23.

libusb on Windows isn't really safe to use from different threads
with a single context.

Source/Core/Common/CMakeLists.txt

@@ -40,11 +40,6 @@ set(SRCS
   Logging/LogManager.cpp
 )
 
-if(LIBUSB_FOUND)
-  set(LIBS ${LIBS} ${LIBUSB_LIBRARIES})
-  set(SRCS ${SRCS} LibusbContext.cpp)
-endif(LIBUSB_FOUND)
-
 if(ANDROID)
   set(SRCS ${SRCS}
     Logging/ConsoleListenerDroid.cpp)