Use canonical `Monad` instance

brittany.cabal

@@ -93,7 +93,6 @@ library {
     -Wno-missing-local-signatures
     -Wno-missing-safe-haskell-mode
     -Wno-monomorphism-restriction
-    -Wno-noncanonical-monad-instances
     -Wno-noncanonical-monoid-instances
     -Wno-prepositive-qualified-module
     -Wno-redundant-constraints

src/Language/Haskell/Brittany/Internal/PreludeUtils.hs

@@ -23,7 +23,6 @@ instance Applicative Strict.Maybe where
   _ <*> _ = Strict.Nothing
 
 instance Monad Strict.Maybe where
-  return = Strict.Just
   Strict.Nothing >>= _ = Strict.Nothing
   Strict.Just x >>= f = f x