Remove incorrect proof about Jemalloc (#3982)

* Remove incorrect proof about Jemalloc

The truth is that Jemalloc is not always the default allocator. This is
only true for the polkadot binary.

* Fmt

* Rephrase

node/overseer/src/lib.rs

@@ -518,18 +518,36 @@ where
 	}
 	let subsystem_meters = overseer.map_subsystems(ExtractNameAndMeters);
 
-	let memory_stats =
-		MemoryAllocationTracker::new().expect("Jemalloc is the default allocator. qed");
-
-	let metronome = Metronome::new(std::time::Duration::from_millis(950)).for_each(move |_| {
-		match memory_stats.snapshot() {
-			Ok(memory_stats_snapshot) => {
-				tracing::trace!(target: LOG_TARGET, "memory_stats: {:?}", &memory_stats_snapshot);
-				metronome_metrics.memory_stats_snapshot(memory_stats_snapshot);
+	let collect_memory_stats: Box<dyn Fn(&OverseerMetrics) + Send> =
+		match MemoryAllocationTracker::new() {
+			Ok(memory_stats) =>
+				Box::new(move |metrics: &OverseerMetrics| match memory_stats.snapshot() {
+					Ok(memory_stats_snapshot) => {
+						tracing::trace!(
+							target: LOG_TARGET,
+							"memory_stats: {:?}",
+							&memory_stats_snapshot
+						);
+						metrics.memory_stats_snapshot(memory_stats_snapshot);
+					},
+					Err(e) => tracing::debug!(
+						target: LOG_TARGET,
+						"Failed to obtain memory stats: {:?}",
+						e
+					),
+				}),
+			Err(_) => {
+				tracing::debug!(
+					target: LOG_TARGET,
+					"Memory allocation tracking is not supported by the allocator.",
+				);
+
+				Box::new(|_| {})
 			},
+		};
 
-			Err(e) => tracing::debug!(target: LOG_TARGET, "Failed to obtain memory stats: {:?}", e),
-		}
+	let metronome = Metronome::new(std::time::Duration::from_millis(950)).for_each(move |_| {
+		collect_memory_stats(&metronome_metrics);
 
 		// We combine the amount of messages from subsystems to the overseer
 		// as well as the amount of messages from external sources to the overseer