drop redundant constraint

Cabal/tests/UnitTests/Distribution/System.hs

@@ -9,7 +9,7 @@ import Distribution.System
 import Test.Tasty
 import Test.Tasty.QuickCheck
 
-textRoundtrip :: (Arbitrary a, Show a, Eq a, Text a) => a -> Property
+textRoundtrip :: (Show a, Eq a, Text a) => a -> Property
 textRoundtrip x = simpleParse (display x) === Just x
 
 tests :: [TestTree]
@@ -26,4 +26,4 @@ instance Arbitrary Arch where
     arbitrary = elements knownArches
 
 instance Arbitrary Platform where
-    arbitrary = liftM2 Platform arbitrary arbitrary
\ No newline at end of file
+    arbitrary = liftM2 Platform arbitrary arbitrary