WIP: remove RUBY_EXTERN from pycall_pyptr_data_type

Author: mrkn

ext/pycall/pycall_internal.h

@@ -663,7 +663,7 @@ Py_ssize_t pycall_python_hexversion(void);
 
 void pycall_Py_DecRef(PyObject *);
 
-RUBY_EXTERN const rb_data_type_t pycall_pyptr_data_type;
+extern const rb_data_type_t pycall_pyptr_data_type;
 size_t pycall_pyptr_memsize(void const *);
 void pycall_pyptr_free(void *);