Revert "windows: better looking titlebar" and follow-up (#9392)

This reverts #9053 and #9375 because they introduced a regression on
`main` that broke the titlebars on macOS:


![image](https://github.com/zed-industries/zed/assets/1185253/d046003b-5c66-4a42-9385-623f5d58c9a4)

Two things are off:

- Left padding is missing
- Titlebar height is less than it was before, which means the
traffic-light buttons are not centered vertically

What @as-cii and I noticed while looking into this: the `cfg!(macos)`
macros that were used don't work like that. You need to check for
`cfg!(target = "macos")` etc. Means that on macOS we never used the
macOS-specific code because the condition was always false.

Overall height, we're not sure about.

Release Notes:

- N/A

crates/ui/src/components.rs

@@ -9,7 +9,6 @@ mod indicator;
 mod keybinding;
 mod label;
 mod list;
-mod platform_titlebar;
 mod popover;
 mod popover_menu;
 mod right_click_menu;
@@ -32,7 +31,6 @@ pub use indicator::*;
 pub use keybinding::*;
 pub use label::*;
 pub use list::*;
-pub use platform_titlebar::*;
 pub use popover::*;
 pub use popover_menu::*;
 pub use right_click_menu::*;