Procedure UnInstallBGIMouse

    This restores the mouse control to  the mouse driver.  This is called
    automatically  when  you  exit  your   program  if  you  have  called
    InstallBGIMouse and have not called this procedure.

    If you created a mask and  picture  for the driver it is up to you to
    release the memory from the heap (if you defined it on the heap).