Remove super old deprecation error

Author: adamwathan

src/index.js

@@ -66,9 +66,4 @@ const plugin = postcss.plugin('tailwind', config => {
   ])
 })
 
-plugin.defaultConfig = function() {
-  // prettier-ignore
-  throw new Error("`require('tailwindcss').defaultConfig()` is no longer a function, access it instead as `require('tailwindcss/defaultConfig')()`.")
-}
-
 module.exports = plugin