Remove proxy-middleware if it no longer in use

[Fydon]

Overview of the issue

Development depencency proxy-middleware seems to no longer be in use. It is only used in Angular.

Motivation for or Use Case

It used to be used by gulp, but I can't see where it is used now. If it isn't used then I could create a pull request to remove it.

Reproduce the error

N/A

Related issues

None found

Suggest a Fix

Remove proxy-middleware from Angular package.json.ejs.

JHipster Version(s)

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JHipster configuration

.yo-rc.json file

{
  "generator-jhipster": {
    "promptValues": {
      "packageName": "com.example",
      "nativeLanguage": "en"
    },
    "jhipsterVersion": "5.5.0",
    "applicationType": "monolith",
    "baseName": "example",
    "packageName": "com.example",
    "packageFolder": "com/example",
    "serverPort": "8080",
    "authenticationType": "jwt",
    "cacheProvider": "ehcache",
    "enableHibernateCache": true,
    "websocket": "spring-websocket",
    "databaseType": "sql",
    "devDatabaseType": "oracle",
    "prodDatabaseType": "oracle",
    "searchEngine": false,
    "messageBroker": false,
    "serviceDiscoveryType": "eureka",
    "buildTool": "gradle",
    "enableSwaggerCodegen": false,
    "jwtSecretKey": "",
    "clientFramework": "angularX",
    "useSass": true,
    "clientPackageManager": "npm",
    "testFrameworks": [
      "gatling",
      "protractor"
    ],
    "jhiPrefix": "jhi",
    "enableTranslation": true,
    "nativeLanguage": "en",
    "languages": [
      "en"
    ]
  }
}

Entity configuration(s) entityName.json files generated in the .jhipster directory

JDL entity definitions

Browsers and Operating System

java version "1.8.0_192"
Java(TM) SE Runtime Environment (build 1.8.0_192-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.192-b12, mixed mode)

git version 2.17.1.windows.2

node: v10.13.0

npm: 6.4.1

yeoman: 2.0.5

Docker version 18.06.1-ce, build e68fc7a

docker-compose version 1.22.0, build f46880fe

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