Remove `t_ptr_Xd` after single-precision changes are merged

After single-precision changes introduced in !98 (merged) , there are now 4 types of t_ptr for each dimension. Example 2d pointers:

1. t_ptr_2d - replaced with t_ptr_2d_dp/t_ptr_2d_wp in ICON and then removed from fortran-support
2. t_ptr_2d_dp
3. t_ptr_2d_sp
4. t_ptr_2d_wp

Same applies to t_ptr_1d,t_ptr_2d,t_ptr_3d,t_ptr_4d.