Updated deprecated cell in ElasticityProblem

src/elasticity/assemble/DGElasticity.cpp

src/elasticity/assemble/EGElasticity.cpp

src/elasticity/assemble/LagrangeElasticity.cpp

src/elasticity/problem/DynamicBoundaryProblems.cpp

src/elasticity/problem/DynamicBoundaryProblems.hpp

src/elasticity/problem/ElasticityBenchmarkProblem.hpp

src/elasticity/problem/ElasticityDebugProblem.hpp

src/elasticity/problem/ElasticityProblem.hpp

src/elasticity/problem/TShapeProblem.cpp

src/elasticity/problem/TShapeProblem.hpp