Update Qiskit Nature benchmarks

[mrossinek]

What is the expected enhancement?

Yesterday, Qiskit Nature merged a major code restructuring PR (https://github.com/Qiskit/qiskit-nature/pull/746). In order to be able to track the performance improvement during active development, the benchmarks should be updated to use the code from the new location. Out of the currently existing benchmarks, only the mapper benchmarks are affected by this.