Removed ExecutionWholeArray class

ExecutionWholeArray is an archaic class in VTK-m that is a thin wrapper around an array portal. In the early days of VTK-m, this class was used to transfer whole arrays to the execution environment. However, now the supported method is to use WholeArray* tags in the ControlSignature of a worklet.

Nevertheless, the WholeArray* tags caused the array portal transferred to the worklet to be wrapped inside of an ExecutionWholeArray class. This is unnecessary and can cause confusion about the types of data being used.

Most code is unaffected by this change. Some code that had to work around the issue of the portal wrapped in another class used the GetPortal method which is no longer needed (for obvious reasons). One extra feature that ExecutionWholeArray had was that it provided an subscript operator (somewhat incorrectly). Thus, any use of '[..]' to index the array portal have to be changed to use the Get method.