Remove svg from file-loader and let it land on userland

[swashata]

There are just too many options for loading svg with webpack and all of them are good. So let's not provide any and remove svg from file-loader.

Rather document some of the best loaders for userland.

• https://github.com/rpominov/svgo-loader
• https://github.com/smooth-code/svgr/tree/master/packages/webpack
• https://webpack.js.org/loaders/svg-inline-loader/