Remove --legacy-linker #2126
Description
Proposed change: Remove support to --legacy-linker. As far as I know, no user should be using --legacy-linker anymore. Internally, we still use it for testing codegen of crates that don't have harnesses. We should start using assess for that or other existing facilities.
Motivation: The legacy linker requires special handling inside kani-driver which is no longer needed. This will simplify some of the code.