#1536 Remove MatrixOperations that were half baked
Some operations (CholeskyFactor, MatMatSolve, LUFactor and GetOrdering) were put in the MatrixOperations file, but they were never used and with the exception of the latests none got a functioning test.
As they are mostly wrappers over PETSc calls, I will decommission them - it will be easy to reintroduce the ones we need, and at that moment we will figure out the associated tests (and also probably a better API - current one exposed PETSc stuff such as IS that we do not use in MoReFEM).