move spack page from e4s into build tools

@kellyrowland @brandon_cook @jscook2345 @etpalmer63

This MR will fix #473 (closed) by moving spack page from E4S into build-tools/spack. I deleted the entire page, there was alot of documentation that is not necessary for us to explain to user and I think it best to reference official spack docs.

With this change, the link will still work since several other pages reference this location (build-tools/spack).