google_ai: Remove list of supported countries (#29348)

This PR removes the list of supported countries from the `google_ai`
crate, as it is no longer referenced in this repo.

Release Notes:

- N/A

crates/google_ai/src/google_ai.rs

@@ -1,12 +1,8 @@
-mod supported_countries;
-
 use anyhow::{Result, anyhow, bail};
 use futures::{AsyncBufReadExt, AsyncReadExt, StreamExt, io::BufReader, stream::BoxStream};
 use http_client::{AsyncBody, HttpClient, Method, Request as HttpRequest};
 use serde::{Deserialize, Serialize};
 
-pub use supported_countries::*;
-
 pub const API_URL: &str = "https://generativelanguage.googleapis.com";
 
 pub async fn stream_generate_content(