Remove duplicate items from Guild.features' documentation

[LikeLakers2]

Hi! There really isn't much to this PR - it's just a documentation fix.

Specifically, in serenity::model::guild::Guild, the documentation for Guild.features featured a list of guild features - including three list items that were duplicates of previous items. This PR removes those three duplicates.

[jamesbt365]

Can't speak for others but we should just remove the list of features, users can refer to the official discord docs or https://docs.discord.food (don't link this tho) for a list of features.

The official docs list is incomplete but contains enough for the common usecases, we shouldn't try and mirror the docs there to here.

[LikeLakers2]

@jamesbt365 Do you want me to wait to see what others say on the matter, or do you want me to remove the rest of the items?

[GnomedDev]

I agree with James, we should remove the raw list of features and just link to the discord documentation for that. I would also like to see a subtitle like "These are user-invisible options which are used for Discord rollouts and/or paid benefits" or something like that.

[LikeLakers2]

So am I removing the rest of the items? Or is this planning for a future PR?