Make connectivity structures trivially copyable

It always worked to trivially copy these classes, but the compiler did
not think so because copy constructors were defined. Change these
constructors to be default so that the compler can properly check
triviality.

vtkm/exec/ConnectivityPermuted.h

@@ -27,13 +27,7 @@ class ConnectivityPermutedVisitCellsWithPoints
 public:
   using SchedulingRangeType = typename OriginalConnectivity::SchedulingRangeType;
 
-  VTKM_SUPPRESS_EXEC_WARNINGS
+  ConnectivityPermutedVisitCellsWithPoints() = default;
-  VTKM_EXEC_CONT
-  ConnectivityPermutedVisitCellsWithPoints()
-    : Portal()
-    , Connectivity()
-  {
-  }
 
   VTKM_EXEC_CONT
   ConnectivityPermutedVisitCellsWithPoints(const PermutationPortal& portal,
@@ -43,12 +37,8 @@ public:
   {
   }
 
-  VTKM_EXEC_CONT
+  ConnectivityPermutedVisitCellsWithPoints(const ConnectivityPermutedVisitCellsWithPoints& src) =
-  ConnectivityPermutedVisitCellsWithPoints(const ConnectivityPermutedVisitCellsWithPoints& src)
+    default;
-    : Portal(src.Portal)
-    , Connectivity(src.Connectivity)
-  {
-  }
 
   ConnectivityPermutedVisitCellsWithPoints& operator=(
     const ConnectivityPermutedVisitCellsWithPoints& src) = default;

vtkm/exec/ConnectivityStructured.h

@@ -34,11 +34,7 @@ class ConnectivityStructured
 public:
   using SchedulingRangeType = typename InternalsType::SchedulingRangeType;
 
-  VTKM_EXEC_CONT
+  ConnectivityStructured() = default;
-  ConnectivityStructured()
-    : Internals()
-  {
-  }
 
   VTKM_EXEC_CONT
   ConnectivityStructured(const InternalsType& src)
@@ -46,11 +42,7 @@ public:
   {
   }
 
-  VTKM_EXEC_CONT
+  ConnectivityStructured(const ConnectivityStructured& src) = default;
-  ConnectivityStructured(const ConnectivityStructured& src)
-    : Internals(src.Internals)
-  {
-  }
 
   VTKM_EXEC_CONT
   ConnectivityStructured(