GDScriptCache: Clear abandoned parser refs

[rune-scape]

regression from #90601

keeps track of GDScriptParserRefs that have been removed from the cache and clears them in all the same places as the true parser refs

avoids leaking these GDScriptParserRefs when they have cyclic refs to each other

[akien-mga]

I'm no GDScript expert but it looks simple enough, and as it's a regression fix I'd like it included in the imminent 4.3 RC 1 build.

Post-merge review from the GDScript team would still be welcome.

[akien-mga]

Thanks!