Remove deprecated introspection.isinstancemethod() and introspection.find_mod_objs() - #19770

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Thanks! Looks good at a glance but will have to re-review again when the time comes when we can actually merge this. Will just have to let this sit for now.

Hi humans 👋 - this pull request hasn't had any new commits for approximately 5 months. I plan to close this in a month if the pull request doesn't have any new commits by then.

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