Remove memory allocation for Item->Node connectivity with legacy connectivities

[grospelliergilles]

Currently ItemSharedInfo always allocate memory for nodes based on ItemTypeInfo::nbLocalNode(). These connectivities are no longer used so we can remove them. But doing that with the current version of Arcane implies incompatibilities with checkpoints:

• [x] The last version of Arcane add version information in checkpoint (done in 20b603c5baece6c5ccf)
• [ ] When everybody will use that version, remove node connectivity allocation.