No longer use brigand

Remove brigand.hpp from VTK-m's source and all references to it. This was declared in an internal directory, so making this backward-incompatible changes should be OK.

Brigand is a third-party library to support template meta-programming. Over the years, we have had to make a few modifications to make sure it compiles with all compilers supported by VTK-m. Unfortunately, because brigand was added before our standard third-party library management was set up, these changes are not managed well. Thus, we cannot easily update with any changes from the project. Thus, our version is slowly diverging from the original, and maintaining it is a hassle.

Also, we have been using brigand less and less throughout the years. Now that we have moved on to C++11 (and now C++14) with variadic templates and other useful std features, the features of brigand have become less critical. Thus, we have implemented all the features we need from brigand internally and have moved our code away from using it.