Remove useless #defines and incorrect claims from header files.

The various __need_* macros were write-only.

Change-Id: Id3cca34188e0801fdf93a038b22f2817226ad9c2
diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index 1361ff5..b46985b 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -31,16 +31,11 @@
 #include <sys/cdefs.h>
 #include <stdio.h>
 
-/* wchar_t is required in stdlib.h according to POSIX */
-#define __need___wchar_t
-#include <stddef.h>
-
 #include <stdarg.h>
+#include <stddef.h>
 #include <time.h>
 #include <malloc.h>
 
-#include <stddef.h>
-
 /* IMPORTANT: Any code that relies on wide character support is essentially
  *            non-portable and/or broken. the only reason this header exist
  *            is because I'm really a nice guy. However, I'm not nice enough