Remove related multimedia ng_banner template

[pspanja]

Related multimedia template for ng_banner uses block content which can't work correctly in the current related multimedia items implementation. I traced the change to removal of linkable.html.twig, which should mean it has not been working for almost 5 years.

If the proof is in the pudding it seems we don't really need this and it's safe to remove it.

[emodric]

~Are you sure about this? I don't see any mention of linkable.html.twig in the deleted file?~

EDIT: Disregard, I misunderstood your point.

[pspanja]

Thanks @emodric