agent: fix unused_parens lint and stop hiding the warning

Fixes: #1359

Signed-off-by: Tim Zhang <tim@hyper.sh>

src/agent/src/main.rs

@@ -4,7 +4,6 @@
 //
 
 #![allow(non_camel_case_types)]
-#![allow(unused_parens)]
 #[macro_use]
 extern crate lazy_static;
 extern crate oci;

src/agent/src/sandbox.rs

@@ -380,7 +380,7 @@ fn online_cpus(logger: &Logger, num: i32) -> Result<i32> {
             logger,
             SYSFS_CPU_ONLINE_PATH,
             r"cpu[0-9]+",
-            (num - onlined_count),
+            num - onlined_count,
         );
         if r.is_err() {
             return r;