Drop `rfm.*` and `sn.*` decorators that are now also exposed as class builtins.

All the decorators below need to go 🪚 in 4.0
- `rfm.run_before`
- `rfm.run_after`
- `rfm.require_deps`
- `rfm.final`
- `rfm.requred_version`
- `sn.sanity_function`