Remove redundant assertion in freeTempLocal (#2313)

Author: ApsarasX

NOTICE

@@ -47,6 +47,7 @@ under the licensing terms detailed in LICENSE:
 * Yasushi Ando <andyjpn@gmail.com>
 * Syed Jafri <syed@metalpay.co>
 * Peter Hayman <peteyhayman@gmail.com>
+* ApsarasX <apsarax@outlook.com>
 
 Portions of this software are derived from third-party works licensed under
 the following terms:

src/flow.ts

@@ -447,7 +447,6 @@ export class Flow {
       }
       default: throw new Error("concrete type expected");
     }
-    assert(local.index >= 0);
     temps.push(local);
   }