Executor: Remove LegacyInstanceReuse strategy (#1486)

It seems the old strategy have been depracted more than one year. 
So maybe it's time to clean up old strategy for wasm executor.


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polkadot address: 15ouFh2SHpGbHtDPsJ6cXQfes9Cx1gEFnJJsJVqPGzBSTudr

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Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: Koute <koute@users.noreply.github.com>

substrate/client/executor/src/integration_tests/mod.rs

@@ -16,9 +16,6 @@
 // You should have received a copy of the GNU General Public License
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
-#[cfg(target_os = "linux")]
-mod linux;
-
 use assert_matches::assert_matches;
 use codec::{Decode, Encode};
 use sc_executor_common::{
@@ -81,14 +78,6 @@ macro_rules! test_wasm_execution {
 					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::Pooling
 				});
 			}
-
-			#[test]
-			fn [<$method_name _compiled_legacy_instance_reuse>]() {
-				let _ = sp_tracing::try_init_simple();
-				$method_name(WasmExecutionMethod::Compiled {
-					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::LegacyInstanceReuse
-				});
-			}
 		}
 	};
 }