Remove unnecessary fields from the tool schemas (#29381)

This PR removes two fields from JSON schemas (`$schema` and `title`),
which are not expected by any model provider, but were spuriously
included by our JSON schema library, `schemars`.

These added noise to requests and cost wasted input tokens.

### Old

```json
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "FetchToolInput",
  "type": "object",
  "required": [
    "url"
  ],
  "properties": {
    "url": {
      "description": "The URL to fetch.",
      "type": "string"
    }
  }
}
```

### New:

```json
{
  "properties": {
    "url": {
      "description": "The URL to fetch.",
      "type": "string"
    }
  },
  "required": [
    "url"
  ],
  "type": "object"
}
```

- N/A

crates/assistant_tools/src/assistant_tools.rs

@@ -110,11 +110,38 @@ pub fn init(http_client: Arc<HttpClientWithUrl>, cx: &mut App) {
 
 #[cfg(test)]
 mod tests {
+    use super::*;
     use client::Client;
     use clock::FakeSystemClock;
     use http_client::FakeHttpClient;
+    use schemars::JsonSchema;
+    use serde::Serialize;
 
-    use super::*;
+    #[test]
+    fn test_json_schema() {
+        #[derive(Serialize, JsonSchema)]
+        struct GetWeatherTool {
+            location: String,
+        }
+
+        let schema = schema::json_schema_for::<GetWeatherTool>(
+            language_model::LanguageModelToolSchemaFormat::JsonSchema,
+        )
+        .unwrap();
+
+        assert_eq!(
+            schema,
+            serde_json::json!({
+                "type": "object",
+                "properties": {
+                    "location": {
+                        "type": "string"
+                    }
+                },
+                "required": ["location"],
+            })
+        );
+    }
 
     #[gpui::test]
     fn test_builtin_tool_schema_compatibility(cx: &mut App) {