Remove the internal `PDFScriptingManager._pageEventsReady` boolean (PR 13074 follow-up)
Remove the internal `PDFScriptingManager._pageEventsReady` boolean (PR 13074 follow-up)

With the introduction of `PDFScriptingManager._closeCapability` in PR 13074, the pre-existing `PDFScriptingManager._pageEventsReady` boolean essentially became redundant.
Given that you always want to avoid tracking closely related state *separately*, since it's easy to introduce subtle bugs that way, we should just remove `PDFScriptingManager._pageEventsReady` now.

Obviously I *should* have done this already back in PR 13074, sorry about the churn here!

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