Remove magnetic field service from TrkVertexFitterUtils and TrkVertexSeedFinderUtils (ATLASRECTS-5442 and ATLASRECTS-5443)
Migrate field service to AtlasFieldCacheCondObj. Update reference files for unit tests where necessary.
(ATLASRECTS-5442 and ATLASRECTS-5443 subtasks of ATLASRECTS-5439)