PVF: Remove artifact persistence across restarts (#2895)

Considering the complexity of
https://github.com/paritytech/polkadot-sdk/pull/2871 and the discussion
therein, as well as the further complexity introduced by the hardening
in https://github.com/paritytech/polkadot-sdk/pull/2742, as well as the
eventual replacement of wasmtime by PolkaVM, it seems best to remove
this persistence as it is creating more problems than it solves.

## Related

Closes https://github.com/paritytech/polkadot-sdk/issues/2863

polkadot/node/core/pvf/tests/it/main.rs

@@ -358,6 +358,25 @@ async fn deleting_prepared_artifact_does_not_dispute() {
 	}
 }
 
+#[tokio::test]
+async fn cache_cleared_on_startup() {
+	// Don't drop this host, it owns the `TempDir` which gets cleared on drop.
+	let host = TestHost::new().await;
+
+	let _stats = host.precheck_pvf(halt::wasm_binary_unwrap(), Default::default()).await.unwrap();
+
+	// The cache dir should contain one artifact and one worker dir.
+	let cache_dir = host.cache_dir.path().to_owned();
+	assert_eq!(std::fs::read_dir(&cache_dir).unwrap().count(), 2);
+
+	// Start a new host, previous artifact should be cleared.
+	let _host = TestHost::new_with_config(|cfg| {
+		cfg.cache_path = cache_dir.clone();
+	})
+	.await;
+	assert_eq!(std::fs::read_dir(&cache_dir).unwrap().count(), 0);
+}
+
 // This test checks if the adder parachain runtime can be prepared with 10Mb preparation memory
 // limit enforced. At the moment of writing, the limit if far enough to prepare the PVF. If it
 // starts failing, either Wasmtime version has changed, or the PVF code itself has changed, and