make PatPV3DFuture independent of beam spot position
as @decianm pointed out, PatPV3DFuture uses the beam spot position https://gitlab.cern.ch/lhcb/Rec/-/blob/master/Tr/PatPV/src/PatPV3DFuture.cpp#L241
however, the reason this algorithm was not phased out in favour of TrackBeamlineVertexFinder was to have a PV reconstruction algorithm available without any assumption on the beam spot position. In practice, this means that the seeding part should be like the one from PVSeed3DTool and not PVSeedTool (the 3D in PatPV3DFuture is at least partially responsible why I was under the misconception that it was already not using the beam spot position)