Remove unused internal _Py_REF_IS_QUEUED() function

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The function was added by commit 6dfb8fe:

commit 6dfb8fe0236718e9afc8136ff2b58dcfbc182022
Author: Sam Gross <colesbury@gmail.com>
Date:   Mon Oct 30 12:06:09 2023 -0400

    gh-110481: Implement biased reference counting (gh-110764)

But the function was never called.

cc @colesbury