Clean up the partitioner for the FEM solver. #8278

Job	Run time
Build SU2 (asan) (BaseNoMPI-asan)	15m 51s
Build SU2 (BaseMPI)	12m 55s
Build SU2 (asan) (ReverseNoMPI-asan)	9m 42s
Build SU2 (ReverseMPI)	4m 39s
Build SU2 (tsan) (BaseOMP-tsan)	11m 32s
Build SU2 (tsan) (ReverseOMP-tsan)	7m 50s
Build SU2 (ForwardMPI)	6m 32s
Build SU2 (BaseNoMPI)	8m 7s
Build SU2 (ReverseNoMPI)	4m 41s
Build SU2 (ForwardNoMPI)	3m 51s
Build SU2 (BaseOMP)	7m 50s
Build SU2 (ReverseOMP)	4m 4s
Build SU2 (ForwardOMP)	3m 18s
Thread Sanitizer Tests	0s
Regression Tests	0s
Unit Tests	0s
Address Sanitizer Tests	0s
	1h 40m 52s

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