Revert "Use livekit's Rust SDK instead of their swift SDK (#13343)" (#20809)

Issues found:

* audio does not work well with various set-ups using USB
* switching audio during initial join may leave the client with no audio
at all
* audio streaming is done on the main thread, beachballing certain
set-ups
* worse screenshare quality (seems that there's no dynamic scaling
anymore, compared to the Swift SDK)

This reverts commit 1235d0808e.

Release Notes:

- N/A

crates/gpui/src/platform/linux.rs

@@ -20,5 +20,3 @@ pub(crate) use text_system::*;
 pub(crate) use wayland::*;
 #[cfg(feature = "x11")]
 pub(crate) use x11::*;
-
-pub(crate) type PlatformScreenCaptureFrame = ();