Removed unused variables in cython gravmag.prism
Removed unused variables in cython gravmag.prism

cmeessen/fatiando,mtb-za/fatiando,fatiando/fatiando,rafaelmds/fatiando,eusoubrasileiro/fatiando_seismic,drandykass/fatiando,fatiando/fatiando,victortxa/fatiando,eusoubrasileiro/fatiando,eusoubrasileiro/fatiando,eusoubrasileiro/fatiando_seismic,drandykass/fatiando,victortxa/fatiando,santis19/fatiando,mtb-za/fatiando,santis19/fatiando,cmeessen/fatiando,rafaelmds/fatiando,eusoubrasileiro/fatiando