quic: remove undefined variable

The `reason` variable never gets defined. It's use in a template string
will always end up as the string `'undefined'`.

PR-URL: #35007
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/internal/quic/core.js

@@ -2389,7 +2389,6 @@ class QuicClientSession extends QuicSession {
 
     // If handle is a number, creating the session failed.
     if (typeof handle === 'number') {
-      let reason;
       switch (handle) {
         case ERR_FAILED_TO_CREATE_SESSION:
           throw new ERR_QUIC_FAILED_TO_CREATE_SESSION();
@@ -2398,7 +2397,7 @@ class QuicClientSession extends QuicSession {
         case ERR_INVALID_TLS_SESSION_TICKET:
           throw new ERR_QUIC_INVALID_TLS_SESSION_TICKET();
         default:
-          throw new ERR_OPERATION_FAILED(`Unspecified reason [${reason}]`);
+          throw new ERR_OPERATION_FAILED(`Unspecified reason [${handle}]`);
       }
     }