Remove fibers dependency recommendation

As of April 2021 maintainers of `fibers` announced it does not work with the current LTS version of Node (16.x) and "[recommends you avoid its use if possible](https://github.com/laverdet/node-fibers/blob/8f2809869cc92c28c92880c4a38317ae3dbe654d/README.md?plain=1#L1)". The authors README.md commit titled "[the end](laverdet/node-fibers@8f28098)" along with the verbiage "inevitable that one day this library will abruptly stop working and no one will be able to do anything about it" suggest this package will not be maintained going forward.

Other benefits of the change:
- Bring this page into alignment with [The Nuxt Configuration Guide](https://nuxtjs.org/docs/features/configuration/) which does not suggest users install fibers.
- Reduce [startup headaches](laverdet/node-fibers#451) for users creating new projects using the latest LTS version of node.

content/en/docs/5.configuration-glossary/5.configuration-css.md

@@ -15,17 +15,13 @@ In case you want to use `sass` make sure that you have installed `sass` and `sas
 
 ::code-group
 ```sh [Yarn]
-yarn add --dev sass sass-loader@10 fibers
+yarn add --dev sass sass-loader@10
 ```
 ```sh [NPM]
-npm install --save-dev sass sass-loader@10 fibers
+npm install --save-dev sass sass-loader@10
 ```
 ::
 
-::alert{type="info"}
-Synchronous compilation with `sass` (2x speed increase) [is enabled automatically](https://github.com/webpack-contrib/sass-loader) when `fibers` is installed.
-::
-
 - Type: `Array`
   - Items: `string`