Simplify livekit config so that cargo check Just Works (#21661)

Supersedes https://github.com/zed-industries/zed/pull/21653

This enables us to use `cargo test -p workspace` on macOS and Linux.

Note that the line diffs in `shared_screen.rs` are spurious, I just
re-ordered the `macos` and `cross-platform` modules to match the order
in the call crate.

Release Notes:

- N/A

crates/call/src/call.rs

@@ -1,41 +1,13 @@
 pub mod call_settings;
 
-#[cfg(any(
-    all(target_os = "macos", feature = "livekit-macos"),
-    all(
-        not(target_os = "macos"),
-        feature = "livekit-macos",
-        not(feature = "livekit-cross-platform")
-    )
-))]
+#[cfg(target_os = "macos")]
 mod macos;
 
-#[cfg(any(
-    all(target_os = "macos", feature = "livekit-macos"),
-    all(
-        not(target_os = "macos"),
-        feature = "livekit-macos",
-        not(feature = "livekit-cross-platform")
-    )
-))]
+#[cfg(target_os = "macos")]
 pub use macos::*;
 
-#[cfg(any(
-    all(
-        target_os = "macos",
-        feature = "livekit-cross-platform",
-        not(feature = "livekit-macos"),
-    ),
-    all(not(target_os = "macos"), feature = "livekit-cross-platform"),
-))]
+#[cfg(not(target_os = "macos"))]
 mod cross_platform;
 
-#[cfg(any(
-    all(
-        target_os = "macos",
-        feature = "livekit-cross-platform",
-        not(feature = "livekit-macos"),
-    ),
-    all(not(target_os = "macos"), feature = "livekit-cross-platform"),
-))]
+#[cfg(not(target_os = "macos"))]
 pub use cross_platform::*;