Variable is assigned but never used

This is just a warning, but elliminating warnings makes the code go cleanly through clang static code analyzer.

c_src/enacl_nif.c

@@ -1167,7 +1167,7 @@ void uint64_pack(unsigned char *y, ErlNifUInt64 x)
 	*y++ = x; x >>= 8;
 	*y++ = x; x >>= 8;
 	*y++ = x; x >>= 8;
-	*y++ = x; x >>= 8;
+	*y++ = x;
 }
 
 static