use BeamSpotData instead of BeamSpotSvc in egammaTrkRefitter : ATLASRECTS-5016

We need to move away from services to conditions data.

• egammaTrkRefitter should now retrieve the relevant BeamSpot ConditionData where applicable
• Since one needs the EventContext to retrieve them, lets pass it to the this tools.
• This means we also need to update the interface
• And the clients so as to pass it.

Since we are here lets also removed an unneeded dynamic_cast and use a bit more the Athena macros.

Mentioning @amorley (original author of the tool)