Name already in use

`contextify_global_private_symbol` is no longer used. It was used
to hold a new context's global object, but the approach has been
changed to hold a ContextifyContext wrapper using
`contextify_context_private_symbol`.

Signed-off-by: Daeyeon Jeong <daeyeon.dev@gmail.com>
PR-URL: #45128
Refs: #44796
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>