all: Don't include system errno.h when it's not needed.

py/reader.c

@@ -71,7 +71,6 @@ void mp_reader_new_mem(mp_reader_t *reader, const byte *buf, size_t len, size_t
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
-#include <errno.h>
 
 typedef struct _mp_reader_posix_t {
     bool close_fd;