[Simulation.Core] Remove dead code - #6298

Some methods in MechanicalOperations can be removed. As a result, the visitors which were used only in those methods can also be removed.

Due to the removal of the visitor MechanicalMultiVectorPeqBaseVectorVisitor, we can consider to deprecate BaseMechanicalState::addFromBaseVectorSameSize.

To do:

• deprecation

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