Remove top level <akka> element

[haighis]

The top level akka element can be removed as well leaving us with:

As well our section name will be hocon?

          <hocon>
          ...
          </hocon>

     </configuration>

[rogeralsing]

This needs to be decided in the core team as removing the name Akka from namespaces and other places would be a major breaking change for Akka users.

[Aaronontheweb]

This is addressed here akkadotnet/akka.net#4128 - keeping the top-level <akka> element for backwards compatibility in that library, but in this one the section can be named whatever you want.