drop oxide branching for the PostCSS plugin for now

This is currently a redirect to the same file, so doesn't hurt.

Author: RobinMalfait

src/index.js

@@ -1,5 +1 @@
-if (process.env.OXIDE) {
-  module.exports = require('./oxide/postcss-plugin')
-} else {
-  module.exports = require('./plugin')
-}
+module.exports = require('./plugin')