Remove unnecessary language extensions

Attempting to abide by the Principle of Least Power. Also: the smaller the
headers in each module are, the happier I am.

src/API.hs

@@ -1,14 +1,9 @@
 {-# LANGUAGE DataKinds #-}
-{-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE LambdaCase #-}
-{-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
 --------------------------------------------------------------------------------
 module API where
 --------------------------------------------------------------------------------
-import Data.Proxy
 import Data.Text
-import Database.Persist
 import Servant.API
 
 import qualified Types as T

src/App.hs

@@ -1,10 +1,5 @@
-{-# LANGUAGE DataKinds #-}
-{-# LANGUAGE DeriveGeneric #-}
-{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TypeApplications #-}
-{-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE TypeOperators #-}
 --------------------------------------------------------------------------------
 module App where
 --------------------------------------------------------------------------------

src/Types.hs

@@ -1,5 +1,3 @@
-{-# LANGUAGE EmptyDataDecls #-}
-{-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE MultiParamTypeClasses #-}