removes grid names from interp_method_file constructor interface

src/core/interp_method_file.c

src/core/interp_method_file.h

src/core/interp_stack_config.c

tests/core/test_interp_method_file_parallel.c

tests/core/test_interp_weights_parallel.c

tests/core/test_interpolation_parallel3.c

tests/core/test_interpolation_parallel4.c

tests/core/test_interpolation_parallel5.c