Remove deprecations from 0.15.x

[bluss]

Remove methods that were deprecated in 0.15.x or earlier.

Remove deprecated (internal) _data_slice

Remove deprecated stack_new_axis

Remove deprecated scalar_sum

Remove deprecated AxisDescription methods

ndarray-rand: Remove deprecated F32

Remove deprecated Zip apply methods

• apply -> for_each
• apply_collect -> map_collect
• apply_assign_into -> map_assign_into
• par_apply -> par_for_each
• par_apply_collect -> par_map_collect
• par_apply_assign_into -> par_map_assign_into

Remove deprecated visit and genrows/gencolumns/_mut

Remove deprecated uninitialized and maybe_uninit