Correct variable name in pyhande.extract.extract_data.
Correct variable name in pyhande.extract.extract_data.

I missed a name change when rebasing/merging
he/pyhande_pop_control_bias, causing extract_data to throw an exception.

hande-qmc/hande,hande-qmc/hande,hande-qmc/hande,hande-qmc/hande,hande-qmc/hande,ruthfranklin/hande