Remove assistant crate (#30168)

This PR removes the `assistant` crate, as it is no longer used.

Release Notes:

- N/A

Cargo.toml

@@ -6,7 +6,6 @@ members = [
     "crates/anthropic",
     "crates/askpass",
     "crates/assets",
-    "crates/assistant",
     "crates/assistant_context_editor",
     "crates/assistant_settings",
     "crates/assistant_slash_command",
@@ -214,7 +213,6 @@ ai = { path = "crates/ai" }
 anthropic = { path = "crates/anthropic" }
 askpass = { path = "crates/askpass" }
 assets = { path = "crates/assets" }
-assistant = { path = "crates/assistant" }
 assistant_context_editor = { path = "crates/assistant_context_editor" }
 assistant_settings = { path = "crates/assistant_settings" }
 assistant_slash_command = { path = "crates/assistant_slash_command" }