docs: WebStorm does not need @angular/language-service anymore (#39637)

Since WebStorm 2019.1, all of Angular Compiler validations has been implemented
as inspections, which has some additional benefits of being able to provide some
basic quick fixes like adding missing selector property, or something as neat as
auto-module import.

See https://intellij-support.jetbrains.com/hc/en-us/community/posts/360009914880

Signed-off-by: Adrien Crivelli <adrien.crivelli@gmail.com>

PR Close #39637

aio/content/guide/language-service.md

@@ -64,36 +64,9 @@ In the marketplace, search for Angular Language Service extension, and click the
 
 ### WebStorm
 
-In [WebStorm](https://www.jetbrains.com/webstorm/), you must install the language service package as a project dependency.
-
-1. Add the following to your `devDependencies` in your project's `package.json`
-
-<code-example language="json" header="package.json">
-devDependencies {
-  "@angular/language-service": "^6.0.0"
-}
-</code-example>
-
-2. In the terminal window at the root of your project, install the `devDependencies` with `npm` or `yarn`:
-
-```sh
-npm install
-```
-*OR*
-
-```sh
-yarn
-```
-
-*OR*
-
-```sh
-yarn install
-```
-
-When Angular sees this dev dependency, it provides the language service in the WebStorm environment.
-WebStorm then gives you colorization inside the template and autocomplete in addition to the Angular Language Service.
+In [WebStorm](https://www.jetbrains.com/webstorm/), enable the plugin [Angular and AngularJS](https://plugins.jetbrains.com/plugin/6971-angular-and-angularjs).
 
+Since WebStorm 2019.1, the `@angular/language-service` is not required anymore and should be removed from your `package.json`.
 
 ### Sublime Text