Remove some of the marketing speak in Core vs Framework article

[cartermp]

#1239 merges an article which provides some guidance for using either .NET Core or .NET Framework for server applications. It was adapted from an internal whitepaper, and thus has a bit of a marketing feel to it. We should rewrite some of the pieces which feel like they're attempting to sell the technology, particularly .NET Core.

[mairaw]

Resolved with #2908