Remove unused allow's (#6760)

These allow's became redundant some time ago so remove them, or address
them if addressing is very simple.

libs/metrics/src/lib.rs

@@ -115,7 +115,6 @@ pub fn set_build_info_metric(revision: &str, build_tag: &str) {
 // performed by the process.
 // We know the size of the block, so we can determine the I/O bytes out of it.
 // The value might be not 100% exact, but should be fine for Prometheus metrics in this case.
-#[allow(clippy::unnecessary_cast)]
 fn update_rusage_metrics() {
     let rusage_stats = get_rusage_stats();