Consolidate Assistant panels in assistant2 feature flag (#23442)

This PR consolidates the two Assistant panels into one for users in the
`assistant2` feature flag.

Now that the Assistant1 prompt editor is accessible through the
Assistant2 panel, we no longer have a need to show both panels.

Release Notes:

- N/A

crates/terminal_view/src/terminal_panel.rs

@@ -42,7 +42,7 @@ use workspace::{
 };
 
 use anyhow::{anyhow, Context, Result};
-use zed_actions::InlineAssist;
+use zed_actions::assistant::InlineAssist;
 
 const TERMINAL_PANEL_KEY: &str = "TerminalPanel";
 

crates/terminal_view/src/terminal_view.rs

@@ -56,7 +56,7 @@ use anyhow::Context;
 use serde::Deserialize;
 use settings::{Settings, SettingsStore};
 use smol::Timer;
-use zed_actions::InlineAssist;
+use zed_actions::assistant::InlineAssist;
 
 use std::{
     cmp,