STYLE: Do not Fill empty OutputVectorPixelType variables in test

`OutputVectorPixelType` is an alias of `VariableLengthVector`, so its instances
are empty, when they are just default-constructed. An attempt to "Fill" such
empty objects has no effect at all.

Modules/Core/Transform/test/itkTransformTest.cxx

@@ -86,9 +86,7 @@ class TransformTestHelper : public Transform<TScalar, VInputDimension, VOutputDi
   OutputVectorPixelType
   TransformVector(const InputVectorPixelType & itkNotUsed(inputVector)) const override
   {
-    OutputVectorPixelType outVector;
-    outVector.Fill(88.8);
-    return outVector;
+    return {};
   }
 
   using Superclass::TransformCovariantVector;
@@ -103,9 +101,7 @@ class TransformTestHelper : public Transform<TScalar, VInputDimension, VOutputDi
   OutputVectorPixelType
   TransformCovariantVector(const InputVectorPixelType & itkNotUsed(inputVector)) const override
   {
-    OutputVectorPixelType outVector;
-    outVector.Fill(6.9);
-    return outVector;
+    return {};
   }
 
   using Superclass::TransformDiffusionTensor3D;
@@ -120,9 +116,7 @@ class TransformTestHelper : public Transform<TScalar, VInputDimension, VOutputDi
   OutputVectorPixelType
   TransformDiffusionTensor3D(const InputVectorPixelType & itkNotUsed(tensor)) const override
   {
-    OutputVectorPixelType outTensor;
-    outTensor.Fill(29.1);
-    return outTensor;
+    return {};
   }
 
   using Superclass::TransformSymmetricSecondRankTensor;
@@ -137,9 +131,7 @@ class TransformTestHelper : public Transform<TScalar, VInputDimension, VOutputDi
   OutputVectorPixelType
   TransformSymmetricSecondRankTensor(const InputVectorPixelType & itkNotUsed(tensor)) const override
   {
-    OutputVectorPixelType outTensor;
-    outTensor.Fill(55.9);
-    return outTensor;
+    return {};
   }
 
   void