Remove unnecessary isFailure method from RateLimiterExecutor

Author: jhalterman

src/main/java/dev/failsafe/internal/RateLimiterExecutor.java

@@ -50,9 +50,4 @@ protected ExecutionResult<R> preExecute() {
       return ExecutionResult.failure(e);
     }
   }
-
-  @Override
-  public boolean isFailure(ExecutionResult<R> result) {
-    return !result.isNonResult() && result.getFailure() instanceof RateLimitExceededException;
-  }
 }