fix(message)!: omit empty Components and Embeds

[AlexeyOplachko]

A while ago there was a small discussion on this topic in discord down from this message
Implemented as was described(at least I think that's what was meant about converting slices to slices of pointers), here's a recording of it working

Snippet with example of code that's used for suppression.

func MessageUpdate(s *discordgo.Session, m *discordgo.MessageUpdate) {
	if len(m.Embeds) > 0 {
		messageEdit := discordgo.NewMessageEdit(m.ChannelID, m.ID)
		messageEdit.Flags = discordgo.MessageFlagsSuppressEmbeds
		s.ChannelMessageEditComplex(messageEdit)
		s.ChannelMessageSend(m.ChannelID, "Suppressed embed")
	}
}

[FedorLap2006]

MessageComponent is an interface. If the array going to consist of pointers, it's going to be extremely inconvenient to pass things in.

var btn discordgo.MessageComponent = discordgo.Button{}
components := []*discordgo.MessageComponent{
    discordgo.Button{...}, // Not possible
    &btn,
}