title: TypeScript linter warning: no-unused-variable is deprecated; but I'm not using this config
body: <p>Today I see this warning in a project being refreshed after 3 months.</p>
  
  <blockquote>
    <p>no-unused-variable is deprecated. Since TypeScript 2.9. Please use the built-in compiler checks instead.</p>
  </blockquote>
  
  <p>But my <code>tsconfig.json</code> does not seem to use this.</p>
  
  <pre><code>{
    "compilerOptions": {
      "lib": ["es6"],
      "module": "commonjs",
      "noImplicitReturns": true,
      "outDir": "lib",
      "sourceMap": true,
      "target": "es6",
      "allowJs" : true
    },
    "compileOnSave": true,
    "include": [
      "src"
    ]
  }
  </code></pre>
  
  <p>Probably it's a config implicit in any of the previous configs. </p>
  
  <p>Could you point me to what to do to fix it?</p>
  
  <p>If usefull</p>
  
  <pre><code>$ node -v
  v10.3.0
  $ npm -v
  6.1.0
  </code></pre>
  
  <p>And these are <code>devDependencies</code> relates to type script in my <code>package.json</code></p>
  
  <pre><code>"devDependencies": {
      ...
      "tslint": "^5.11.0",
      "typescript": "^2.9.1"
      ...
    },
  </code></pre>