Atspi-2.0 GIR contains nonexistent function

The function `atspi_table_cell_get_column_index` is present in the Atspi-2.0 GIR (and the corresponding header), but not in the library. It was removed from the library without updating the header here: https://github.com/GNOME/at-spi2-core/commit/ac5daef64178de2bfc325fe890e35717702ffa3b