removed ZSTD_highbit() from zstd_internal.h, as it is only used by zstd_compress.c

lib/dictBuilder/zdict.c

@@ -60,7 +60,7 @@
 #include "error_private.h"
 #include "fse.h"
 #include "huf_static.h"
-#include "zstd_internal.h"
+#include "zstd_internal.h" /* includes zstd.h */
 #include "xxhash.h"
 #include "divsufsort.h"
 #define ZDICT_STATIC_LINKING_ONLY