Reduce transitive includes

Author: AA-Turner

Modules/_zstd/buffer.h

@@ -5,10 +5,11 @@ Python module.
 
 #ifndef ZSTD_BUFFER_H
 #define ZSTD_BUFFER_H
-#include "_zstdmodule.h"
 #include "Python.h"
 #include "pycore_blocks_output_buffer.h"
 
+#include <zstd.h>                 // ZSTD_outBuffer
+
 /* Blocks output buffer wrapper code */
 
 /* Initialize the buffer, and grow the buffer.