Integrate the comments from the upstream PRs (#442)

Clean up the Patatrack code base following the comments received during the integration into the upstream release.

Currently tracks the changes introduced due to
   - cms-sw#29109: Patatrack integration - trivial changes (1/N)
   - cms-sw#29110: Patatrack integration - common tools (2/N)

List of changes:
 * Remove unused files
 * Fix compilation warnings
 * Fix AtomicPairCounter unit test
 * Rename the cudaCompat namespace to cms::cudacompat
 * Remove extra semicolon
 * Move SimpleVector and VecArray to the cms::cuda namespace
 * Add missing dependency
 * Move HistoContainer, AtomicPairCounter, prefixScan and radixSort to the cms::cuda namespace
 * Remove rule exception for HeterogeneousCore
 * Fix code rule violations:
    - replace using namespace cms::cuda in test/OneToManyAssoc_t.h .
    - add an exception for cudaCompat.h:
      cudaCompat relies on defining equivalent symbols to the CUDA
      intrinsics in the cms::cudacompat namespace, and pulling them in the
      global namespace when compiling device code without CUDA.
* Protect the headers to compile only with a CUDA compiler

SimTracker/TrackerHitAssociation/interface/trackerHitAssociationHeterogeneous.h

@@ -62,7 +62,7 @@ namespace trackerHitAssociationHeterogeneous {
     m_view.n2_d = get32(3);
   }
 
-  using ProductCUDA = Product<cudaCompat::GPUTraits>;
+  using ProductCUDA = Product<cms::cudacompat::GPUTraits>;
 
 }  // namespace trackerHitAssociationHeterogeneous