Remove t_ptr_Xd (no suffix)

What is the change

Removal of t_ptr_{1,2,3,4}d derived-types which do not use suffixes to specify real kind.

Details of the change

• In place of e.g. t_ptr_3d, there are now specific derived types for real kinds t_ptr_3d_dp, t_ptr_3d_sp, t_ptr_3d_wp.
• Use of t_ptr_3d was removed from ICON in https://gitlab.dkrz.de/icon/icon/-/merge_requests/539
• Closes #26 (closed) .