The main change is to remove the use of vtkTemporalDataSet and move
the support of multiple temporal data sets from the execution
pipeline to filters. To be specific,

- Before, a filter can request objects from multiple time steps by
  setting the key UPDATE_TIME_STEPS to a vector of doubles; the
  resulting objects get wrapped by the pipeline into a single
  vtkTemporalDataSet object.

- After, a filter can only ask for a single time step from the
  pipeline by setting the key UPDATE_TIME_STEP to a single double.
  The "wrapping" no longer happens. If a filter want to request
  multiple time steps, it needs to either inherit from
  vtkMultiTimeStepAlgorithm or use the CONTINUE_EXECUTION to loop the
  upstream pipeline and store the data from each iteration.

The following key changes/constants are backward incompatible:

vtkStreamingDemandDrivenPipeline::UPDATE_TIME_STEPS(() ->
   vtkStreamingDemandDrivenPipeline::UPDATE_TIME_STEP((),
   vtkMultiStepAlgorithm::UPATE_TIME_STEPS()

vtkStreamingDemandDrivenPipeline::PREVIOUS_UPDATE_TIME_STEPS() ->
  vtkStreamingDemandDrivenPipeline::PREVIOUS_UPDATE_TIME_STEP()

deleted: vtkCompositeDataPipeline::REQUIRES_TIME_DOWNSTREAM()

depreicated: VTK_TIME_EXTENT

Change-Id: I635b6401ae4f0a7ea7c4b5c466ced40ee75963c7