Don't Copy mobj->dontdrawforviewmobj To MT_OVERLAYs

!2014 (merged) introduced mobj->drawonlyforplayer and mobj->dontdrawforviewmobj variables, to control per-player object visibility.

This merge request simply makes it so that MT_OVERLAY mobjs don't copy their target's dontdrawforviewmobj value every tic (or at all), making it easier to have an overlay with a different dontdrawforviewmobj value if desired.
Reasoning: I just didn't like it. But, equally importantly, MT_OVERLAYs already don't copy their target's drawonlyforplayer (because Tailsbot's flight indicator needs a different drawonlyforplayer value than Tailsbot themselves) - and then, why copy "only one" of these variables, instead of both (not an option) or neither?

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TL;DR: MT_OVERLAYs no longer copy their target's dontdrawforviewmobj value