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/call/Cargo.toml

@@ -27,7 +27,6 @@ anyhow.workspace = true
 audio.workspace = true
 client.workspace = true
 collections.workspace = true
-feature_flags.workspace = true
 fs.workspace = true
 futures.workspace = true
 gpui.workspace = true