Clean up CAHitNtupletHeterogeneousEDProducer (#83)

Apply some clean up to the code and formatting of `CAHitNtupletHeterogeneousEDProducer` and `CAHitQuadrupletGeneratorGPU`, as suggested by @makortel during the review of #48:
  - clean up the `BuildFile.xml`
  - remove unused data members and arguments from function calls;
  - percolate the CUDA stream instead of storing it as a data member.

Also:
  - add `cudaCheck` calls around memory allocations and copies;
  - reduce the number of memory allocations used to set up the GPU state.

RecoPixelVertexing/PixelTriplets/plugins/BuildFile.xml

@@ -1,17 +1,16 @@
-<use   name="RecoTracker/TkTrackingRegions"/>
-<use   name="RecoPixelVertexing/PixelTriplets"/>
-<use   name="RecoTracker/TkSeedingLayers"/>
-<use   name="RecoPixelVertexing/PixelTrackFitting"/>
-<library   file="*.cu *.cc" name="RecoPixelVertexingPixelTripletsPlugins">
-  <use   name="cuda"/>
-  <flags   EDM_PLUGIN="1"/>
-  <flags   CUDA_FLAGS="--expt-relaxed-constexpr"/>
-  <use name="FWCore/Framework"/>
-  <use name="FWCore/PluginManager"/>
-  <use name="FWCore/ParameterSet"/>
-  <use name="HeterogeneousCore/Producer"/>
-  <use name="HeterogeneousCore/Product"/>
-  <use name="HeterogeneousCore/CUDACore"/>
-  <use name="cuda-api-wrappers"/>
+<use name="cuda"/>
+<use name="cuda-api-wrappers"/>
+<use name="FWCore/Framework"/>
+<use name="FWCore/ParameterSet"/>
+<use name="FWCore/PluginManager"/>
+<use name="HeterogeneousCore/CUDACore"/>
+<use name="HeterogeneousCore/Producer"/>
+<use name="HeterogeneousCore/Product"/>
+<use name="RecoPixelVertexing/PixelTrackFitting"/>
+<use name="RecoPixelVertexing/PixelTriplets"/>
+<use name="RecoTracker/TkSeedingLayers"/>
+<use name="RecoTracker/TkTrackingRegions"/>
+<library file="*.cu *.cc" name="RecoPixelVertexingPixelTripletsPlugins">
+  <flags EDM_PLUGIN="1"/>
 </library>
-<flags   CXXFLAGS="-Ofast -fno-math-errno"/>
+<flags CXXFLAGS="-Ofast -fno-math-errno"/>