Sync default legacy skin resources with implementation

[cl8n]

this PR makes the legacy default skin include all resources from stable that are used in lazer, and removes any extras. the only exceptions are seeya and welcome samples, which are coupled with IntroScreen logic in a way that wouldn't make sense for this default skin to be overriding

this makes my work on ppy/osu#20659 a bit easier because I don't have to think about where to draw the line for which textures to include, and also I can have sample lookups fall back from 2007 to 2013 without worry that any 2013 ones will change later on (for example, pause-loop is currently a duplicate of Samples/Gameplay/pause-loop, but that may not be the case forever).

[peppy]

What's the idea here? Remove things we're not using only to add them back when we end up using them?

[tadatomix]

As long as I understand your idea, with deleting sprites, I don't like it. The fact we don't have a countdown yet, doesn't mean we should get rid of it's sprites (I remember I saw a PR, which was implementing countdown on legacy skins already). Same goes to comboburst, since lack of it's current logic doesn't imply it's full removal, in my eyes. Removing samples is related to what I said about sprites.

[cl8n]

What's the idea here? Remove things we're not using only to add them back when we end up using them?

for some of the removals, yes -- the main point of this is finding where to draw the line so that I can decide which files to add for my initial PR of the "2007" default skin, which I want to stay roughly in sync with the 2013 skin. there are a lot of odd cases with these unused files that made me think they were all just accidentally included.

I get what you're saying though, I restored files that seem like they may be used soon:

• countdown (Implement legacy countdown osu#21009)
• combo bursts (Implement legacy combo splash osu#17616)
• geki/katu (i will likely have a PR soon)

and what I mean by some of these "odd cases" in master is...

• star, star3, and taiko-hit300g are included, but won't appear in lazer unless legacy-skinnable versions of their respective screens are implemented, at which point you'd need to include way more textures than just those
• comboburst is included, but its catch and mania friends aren't
• section pass and fail samples are included, but their corresponding textures aren't
  • these samples are also in Samples/Gameplay/, but presumably if they were actually implemented, you'd want them to be redesigned for Argon & Triangles, not borrow the old ones
• pause-retry-click is supported in lazer, but not included in the default legacy skin. oddly none of the other legacy pause click samples are supported...

since lack of it's current logic doesn't imply it's full removal

nor does this PR, I'm only trying to clean up what's here right now

[bdach]

I think I'd prefer not removing any assets, because other than removing star, star3, and taiko-hit300g, I don't really agree with most other removals, and even then, those particular ones heavily depend on how far we're willing to backport stable screens wholesale to lazer. (I don't know the answer to that, but given that it's up in the air, removing things seems a bit counterproductive.)