Revert "Hide most of the implementation of `struct rb_io`. (#6511)"

This reverts commit 18e55fc1e1ec20e8f3166e3059e76c885fc9f8f2.

fix [Bug #19704]
https://bugs.ruby-lang.org/issues/19704
This breaks compatibility for extension libraries. Such changes
need a discussion.

1 files changed, 0 insertions, 1 deletions

diff --git a/process.c b/process.c
index b4435446f0..c54e11860e 100644
--- a/process.c
+++ b/process.c
@@ -103,7 +103,6 @@ int initgroups(const char *, rb_gid_t);
 #include "internal/error.h"
 #include "internal/eval.h"
 #include "internal/hash.h"
-#include "internal/io.h"
 #include "internal/numeric.h"
 #include "internal/object.h"
 #include "internal/process.h"