theme crate spring cleaning (#18695)

This PR does some spring cleaning on the `theme` crate:

- Removed two unused stories and the story dep
- Removed the `one` theme family (from the `theme` crate, not the app),
this is now `zed_default_themes`.
- This will hopefully remove some confusion caused by this theme we
started in rust but didn't end up using
- Removed `theme::prelude` (it just re-exported scale colors, which we
don't use outside `theme`)
- Removed completely unused `zed_pro` themes (we started on these during
the gpui2 port and didn't finish them.)

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/theme/src/settings.rs

@@ -1,4 +1,4 @@
-use crate::one_themes::one_dark;
+use crate::fallback_themes::zed_default_dark;
 use crate::{Appearance, SyntaxTheme, Theme, ThemeRegistry, ThemeStyleContent};
 use anyhow::Result;
 use derive_more::{Deref, DerefMut};
@@ -629,7 +629,7 @@ impl settings::Settings for ThemeSettings {
             theme_selection: defaults.theme.clone(),
             active_theme: themes
                 .get(defaults.theme.as_ref().unwrap().theme(*system_appearance))
-                .or(themes.get(&one_dark().name))
+                .or(themes.get(&zed_default_dark().name))
                 .unwrap(),
             theme_overrides: None,
             ui_density: defaults.ui_density.unwrap_or(UiDensity::Default),