Remove testing headers from benchmarking
The code in `vtkm/cont/Testing.h` now requires a library, which is not built if testing is not built. Thus, the benchmarking code was giving a compile error if benchmarking was on but testing was off. Change the benchmarking to not rely on anything in the Testing framework. This means using classes in `vtkm/source` instead of `MakeTestData`. Also avoid using the `TestValue` defined for the tests. (In one case, we have a simple replacement.) Also had to fix a problem with a header file not defining everything it needed to compile.