Use the same InlineAssist action between both assistant and assistant2 (#22126)

This PR makes it so `assistant` and `assistant2` both use the same
action for inline assist (`zed_actions::InlineAssist`).

This makes it so the keybindings to deploy the inline assist seamlessly
swap based on the feature flag without needing to rebind them.

One minor caveat: if you're using `assistant2` the action name in the
command palette will be `assistant: inline assist`.

Release Notes:

- N/A

crates/assistant/src/assistant_panel.rs

@@ -108,7 +108,6 @@ pub fn init(cx: &mut AppContext) {
 
                     workspace.toggle_panel_focus::<AssistantPanel>(cx);
                 })
-                .register_action(AssistantPanel::inline_assist)
                 .register_action(ContextEditor::quote_selection)
                 .register_action(ContextEditor::insert_selection)
                 .register_action(ContextEditor::copy_code)