@author Wolfgang Kurtz, Guowei He, Mukund Pondkule
@date 03.03.2023
@brief Deallocation of observation index arrays
@details
This subroutine deallocates the observation index arrays used in
subroutine get_obsindex_currentobsfile
.
Only used in enkf_parflow.c
with pf_gwmasking=2
.