Remove arg_ordering legacy code

[sergisiso]

Currently we store 2 duplicated args list: _arglist and _psyir_arglist. After #1010 the former could be eliminated and the append(cell_ref_name) should be fully deleted in favour of the already present psyir_append(cell_ref)

This represent changes in quite a few places because many method return both (str and reference) to populate each list. For example, "cell_ref_name" should be "cell_ref" and only return the Reference. Additionally, all these methods have a "var_accesses" argument. They can now be deleted in favour of doing cell_ref.reference_accesses(...) at the caller site, as all information should be in the tree now.

[sergisiso]

Also, why do we keep state, could not this be done at the beginning (possibly the Collections.declarations and initialisation as well) when we create the PSy-layer and store in the symbol_table.argument_list?

Then we wouldn't need things like

# KernCallArgList creates symbols (sometimes with wrong type), we don't
# want those to be kept in the SymbolTable, so we copy the symbol table
tmp_symtab = self.ancestor(InvokeSchedule).symbol_table.deep_copy()
create_arg_list._forced_symtab = tmp_symtab
create_arg_list.generate(var_accesses)