I) `clear_proxy` parameter was not assigned to parm in RNA define code,
so 'pyfunc optional' flag was set to `new_id` parameter of `user_remap`
func - super ugly!
II) `clear_proxy` parameter itself, when set to False, would allow to
leave .blend file in invalid state (more than one proxy of same object),
this should never, ever be allowed in RNA API imho. Left the PAI
untouched for now, just disabled any effect from this parameter (hence
always clearing proxy when copying).
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