misc: remove once_cell; superseded by std::*

We now have types in the Rust standard library.
Dropping the dependency.

I found this by using the `clippy::pedantic` group.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

event_monitor/src/lib.rs

@@ -8,13 +8,12 @@ use std::collections::HashMap;
 use std::fs::File;
 use std::io;
 use std::os::unix::io::AsRawFd;
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
 use std::time::{Duration, Instant};
 
-use once_cell::sync::OnceCell;
 use serde::Serialize;
 
-static MONITOR: OnceCell<MonitorHandle> = OnceCell::new();
+static MONITOR: OnceLock<MonitorHandle> = OnceLock::new();
 
 #[derive(Serialize)]
 struct Event<'a> {