demon2 -> demon; eliminate original demon layer

src/demon/demon_inc.c

@@ -2,14 +2,9 @@
 // Licensed under the MIT license (https://opensource.org/license/mit/)
 
 #include "demon_core.c"
-#include "demon_common.c"
-#include "demon_accel.c"
-#include "demon_os.c"
 
 #if OS_WINDOWS
-# include "win32/demon_os_win32.c"
-#elif OS_LINUX
-# include "linux/demon_os_linux.c"
+# include "win32/demon_core_win32.c"
 #else
-# error No Demon Implementation for This OS
+# error Demon layer backend not defined for this operating system.
 #endif