Remove beatmap legacy nomination mode

[notbakaneko]

This was kept around when the new beatmapset nomination code was implemented since there were plenty of existing nominations for pending beatmaps, but now there's only 5 pending/wip beatmaps with legacy mode nominations left and they're pretty old nominations

beatmapset_id	created_at
690222	2018-03-06 08:11:31
535792	2018-07-12 19:53:17
749623	2018-08-22 18:19:47
516707	2019-07-17 02:38:58
1031432	2019-09-24 13:55:13

[Hiviexd]

if these nominations need to be reset because of this then that can be arranged. all of them will need to be reset anyways if any were to be pushed to Ranked because of broken rules/guidelines that were made after the maps were abandoned.

[peppy]

What's required to make this happen? I think we should just reset them and get this closed out.

[notbakaneko]

They should just be reset.

[notbakaneko]

Actually, since these all seem to be single mode sets, maybe the modes can just be filled in instead.

[peppy]

I've reset all the remaining beatmaps using the legacy system.

[nanaya]

shouldn't all the codes relating to this also be removed?

[peppy]

I did think that was the plan 🤔

[peppy]

cc @notbakaneko in case you missed this