Fix HeatFlux non-dimensionalization #6814

Job	Run time
Build SU2 (tsan) (BaseOMP-tsan)	24m 40s
Build SU2 (tsan) (ReverseOMP-tsan)	54m 10s
Build SU2 (BaseMPI)	15m 53s
Build SU2 (ReverseMPI)	20m 40s
Build SU2 (ForwardMPI)	16m 34s
Build SU2 (BaseNoMPI)	12m 29s
Build SU2 (ReverseNoMPI)	17m 22s
Build SU2 (ForwardNoMPI)	20m 36s
Build SU2 (BaseOMP)	11m 37s
Build SU2 (ReverseOMP)	28m 6s
Build SU2 (ForwardOMP)	18m 41s
Unit Tests (test_driver)	1m 11s
Unit Tests (test_driver_AD)	1m 29s
Unit Tests (test_driver_DD)	1m 41s
Regression Tests (vandv.py)	2m 55s
Regression Tests (tutorials.py)	5m 44s
Regression Tests (parallel_regression.py)	17m 33s
Regression Tests (parallel_regression_AD.py)	10m 18s
Regression Tests (serial_regression.py)	21m 37s
Regression Tests (serial_regression_AD.py)	7m 8s
Regression Tests (hybrid_regression.py)	14m 51s
Regression Tests (hybrid_regression_AD.py)	5m 31s
Thread Sanitizer Tests (hybrid_regression.py)	32m 46s
Thread Sanitizer Tests (hybrid_regression_AD.py)	14m 49s
	6h 18m 21s

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