Planning: deprecate unused feature generator class

modules/planning/learning_based/feature_generator/BUILD

-load("@rules_cc//cc:defs.bzl", "cc_library")
-load("//tools:cpplint.bzl", "cpplint")
-
-package(default_visibility = ["//visibility:public"])
-
-cc_library(
-    name = "feature_generator",
-    hdrs = ["feature_generator.h"],
-    copts = ["-DMODULE_NAME=\\\"planning\\\""],
-)
-
-cpplint()

modules/planning/learning_based/feature_generator/feature_generator.h

-/******************************************************************************
- * Copyright 2020 The Apollo Authors. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- *****************************************************************************/
-
-/**
- * @file
- * @brief Define the feature generator base class
- */
-
-#pragma once
-
-#include <string>
-
-namespace apollo {
-namespace planning {
-
-class FeatureGenerator {
- public:
-  /**
-   * @brief Constructor
-   */
-  FeatureGenerator() = default;
-
-  /**
-   * @brief Destructor
-   */
-  virtual ~FeatureGenerator() = default;
-
-  /**
-   * @brief Get the name of generator
-   */
-  virtual std::string GetName() = 0;
-
-  /**
-   * @brief generate feature for certain model
-   */
-  virtual bool GenerateFeature() = 0;
-};
-
-}  // namespace planning
-}  // namespace apollo