fixes #4804

Hello.
When using typescript-axios, a warning occurred in unused import.
I tried to fix it, so please take a look if you like.

Before

import { Box } from './box';
import { BoxInBox } from './box-in-box';
import { Response } from './response';

/**
 * 
 * @export
 * @interface BoxesResponse
 */
export interface BoxesResponse {
    /**
     * 
     * @type {string}
     * @memberof BoxesResponse
     */
    status: BoxesResponseStatusEnum;
    /**
     * 
     * @type {number}
     * @memberof BoxesResponse
     */
    id?: number;
    /**
     * 
     * @type {string}
     * @memberof BoxesResponse
     */
    name?: string;
    /**
     * 
     * @type {BoxInBox}
     * @memberof BoxesResponse
     */
    box?: BoxInBox;
}

/**
    * @export
    * @enum {string}
    */
export enum BoxesResponseStatusEnum {
    Success = 'success',
    Error = 'error'
}

After

import { Box } from './box';
import { Response } from './response';

/**
 * 
 * @export
 * @interface BoxesResponse
 */
export type BoxesResponse = Response & Box;

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
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@TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @nicokoenig (2018/09) @topce (2018/10) @akehir (2019/07) @petejohansonxo (2019/11)