cpp_generator::decl_printer::print_persistent_callbacks: range based for-loops
cpp_generator::decl_printer::print_persistent_callbacks: range based for-loops

This is a minor clean-up.

Signed-off-by: Sven Verdoolaege <dd860110a62b19214c4ee03aec0abffecb4e86b8@cerebras.net>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl