gemini: Fix issue when deserializing tool call (#29363)

Fixes a regression introduced in #29322

Release Notes:

- N/A

Co-authored-by: Agus Zubiaga <hi@aguz.me>

crates/google_ai/src/google_ai.rs

@@ -334,7 +334,6 @@ pub struct CountTokensResponse {
 #[derive(Debug, Serialize, Deserialize)]
 pub struct FunctionCall {
     pub name: String,
-    pub raw_args: String,
     pub args: serde_json::Value,
 }