assistant: Unship tool use (#23969)

This PR unships tool use from Assistant1.

This was only ever partially implemented, and was never released to end
users.

Assistant2 will support tool use.

Release Notes:

- N/A

crates/assistant_context_editor/Cargo.toml

@@ -16,14 +16,12 @@ anyhow.workspace = true
 assistant_settings.workspace = true
 assistant_slash_command.workspace = true
 assistant_slash_commands.workspace = true
-assistant_tool.workspace = true
 chrono.workspace = true
 client.workspace = true
 clock.workspace = true
 collections.workspace = true
 context_server.workspace = true
 editor.workspace = true
-feature_flags.workspace = true
 fs.workspace = true
 futures.workspace = true
 fuzzy.workspace = true