[GeoMechanicsApplication] Remove duplicated member functions of SmallStrainUPwDiffOrderElement

[markelov208]

Acceptance Criteria

Member functions that duplicate the functionality as implemented by its new base class (i.e. UPwBaseElement) have been removed.

Implementation Details

The following member functions have been deemed to be duplicates of the base class's ones (i.e. they are identical to the ones of class UPwBaseElement):

• CalculateDampingMatrix
• CalculateIntegrationCoefficient
• CalculateIntegrationCoefficients
• CalculateLeftHandSide
• CalculateLocalSystem
• CalculateOnIntegrationPoints (only the overload that accepts a Variable<ConstitutiveLaw::Pointer> instance)
• CalculateRightHandSide
• EquationIdVector
• GetDofList
• GetFirstDerivativesVector
• GetIntegrationMethod
• GetSecondDerivativesVector
• ResetConstitutiveLaw
• SetValuesOnIntegrationPoints (only the overloads that accept Variable<double> or Variable<Matrix> instances)

If one or more of these functions are not covered, first tests should be added, in a different issue.