Remove /docs slash command (#36325)

This PR removes the `/docs` slash command.

We never fully shipped this—with it requiring explicit opt-in via a
setting—and it doesn't seem like the feature is needed in an agentic
world.

Release Notes:

- Removed the `/docs` slash command.

Cargo.toml

@@ -81,7 +81,6 @@ members = [
     "crates/http_client_tls",
     "crates/icons",
     "crates/image_viewer",
-    "crates/indexed_docs",
     "crates/edit_prediction",
     "crates/edit_prediction_button",
     "crates/inspector_ui",
@@ -305,7 +304,6 @@ http_client = { path = "crates/http_client" }
 http_client_tls = { path = "crates/http_client_tls" }
 icons = { path = "crates/icons" }
 image_viewer = { path = "crates/image_viewer" }
-indexed_docs = { path = "crates/indexed_docs" }
 edit_prediction = { path = "crates/edit_prediction" }
 edit_prediction_button = { path = "crates/edit_prediction_button" }
 inspector_ui = { path = "crates/inspector_ui" }