[LinAlg] Remove inheritance to `Epetra` objects

[maxfirmbach]

Description

We should cut all inheritance to Epetra based objects to make our code more independent of implementation details. This mainly relates to Epetra_Operator.

Cut inheritance to Epetra_Operator from the following classes:

• class LinalgPrecondOperator (see [solver] Move internals to Thyra objects #1400 [Solver] Move LinalgPrecondOperator to Thyra #1642)
• class SparseOperator (related to [LinAlg] Refactor sparse operator, matrix and block-matrix wrapper #863, see [LinAlg] Remove the inheritance of Epetra_Operator from SparseOperator #1524)
  By resolving we propagte down the inheritance to
  • class BlockSparseMatrix
  • class SparseOperatorWrapper (see [LinAlg] Remove the inheritance of Epetra_Operator from SparseOperator #1524)
• class BlockSmootherOperator (related to [Teko] Remove amgnxn framework #754)
• class FSIMatrixFree (related to What to do with ::NOX::Epetra::MatrixFree and ::NOX::Epetra::FiniteDifference #1508, see [LinAlg] Remove the inheritance of Epetra_Operator from SparseOperator #1524)

Possible Solution and Definition of Done

• Remove inheritance of Epetra_Operator of the given classes above

Interested Parties

@vovannikov @knarfnitram @mayrmt