[perl #46703] [TODO] [C] Fix ref_count handling for exception_handlers

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# New Ticket Created by  Paul Cochrane 
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In src/pmc/exception_handler.pmc there is the todo item:

     * can't reuse Continuation's destroy yet -
     * XXX fix ref_count handling for exception_handlers first

So, ref_count handling for exception_handlers needs to be implemented, and
then we can reuse Continuations destroy().  Do this (please).