Remove babelrc from loader-specific options (#667)

`babelrc` is [supported by Babel](https://babeljs.io/docs/en/options#babelrc), so it is not a loader-specific option.

README.md

@@ -88,9 +88,6 @@ This loader also supports the following loader-specific option:
 
 * `cacheIdentifier`: Default is a string composed by the babel-core's version, the babel-loader's version, the contents of .babelrc file if it exists and the value of the environment variable `BABEL_ENV` with a fallback to the `NODE_ENV` environment variable. This can be set to a custom value to force cache busting if the identifier changes.
 
-* `babelrc`: Default `true`. When `false`, no options from `.babelrc` files will be used; only the options passed to
-`babel-loader` will be used.
-
 __Note:__ The `sourceMap` option is ignored, instead sourceMaps are automatically enabled when webpack is configured to use them (via the `devtool` config option).
 
 ## Troubleshooting