Remove deprecated `datapkg` argument from functions

[peterdesmet]

• Entirely remove datapkg as a deprecated alternative argument for package in all functions where it is used
• Remove function_name from check_package(), see this comment #223 (comment)

[PietrH]

the datapkg argument is present in:

• check_package()
• check_species()
• get_cam_op()
• get_custom_effort()
• get_effort()
• get_n_individuals()
• get_n_obs()
• get_n_species()
• get_rai()
• get_record_table()
• get_scientific_name()
• get_species()
• map_dep()
• get_dep_no_obs() (zzz.R)

And tests for:

• check_package()
• get_cam_op()
• get_custom_effort()
• get_effort()
• get_n_individuals()
• get_n_obs()
• get_n_species()
• get_rai_individuals()
• get_rai()
• get_record_table()
• get_scientific_name()
• get_species()
• map_dep()