res_multistep: Fix cfgpp and add ancestral samplers

[pamparamm]

Continuation of #6462
This PR:

• Adds res_multistep_ancestral and res_multistep_ancestral_cfg_pp samplers. Since res_multistep is a modified version of DPM-Solver++, it's quite easy to make it ancestral.
• Fixes cfg_pp implementation in res_multistep sampler by replacing incorrect denoised with uncond_denoised and setting old_denoised to uncond prediction. This should decrease artifacts even more.

I've also removed some unused parts and simplified the code even more.

[eeditor1055]

Good day.
I updated ComfyUI (twice) after this commit merge, but still don't have res_multistep_ancestral and it's cfg_pp variant on Ksampler.

[ltdrdata]

Make sure your ComfyUI is up-to-date.

[eeditor1055]

I run update again. This time it actually updated it. Now I have it. Maybe it was some bug.
Thanks for help