Remove all skin primary key from karaoke object.

[andy840119]

https://miro.com/app/board/uXjVOdFaTlU=/?invite_link_id=425811082676

This is the relationship between every editor and its related object. After declaring the Undefined parts, I noticed that should not place something like LayoutIndex or StyleIndex into lyrics.

There's some reason for it:

• we cannot make sure that one lyric only has one style. it might be able to have more than one.
• maybe other playfield type will not have something like Layout index.
• it will be a pain if add lots of property in lyrics.
• karaoke beatmap should record the things that are very important. means should expect that will not change the format for at least 10 years.

[andy840119]

Another benefit: we can design many skins for single beatmap.