* Removes a bunch of trivial usage of Blazor

... in names and comments where we don't specifically mean Blazor.

* Remove obsolete Startup from Components app

* Move UseBlazor into Blazor.Server

Moves UseBlazor and the related features in Blazor.Server - along with
some other general cleanup of misc shared files.

Now Components.Server has a much slimmer set of dependencies (MVC is
gone) and doesn't contain the "double startup" pattern that we
introduced (sorry).

We'll revisit UseBlazor and the dependencies there once the new
MapFallbackToFile support is available from static files.

* minor PR feedback

* Update reference assemblies

* fix broken test