Move Experimental options to Difficulty Adjust mod

[ziv-vy]

Doesn't make sense IMO to split options which are so similar into two different mods, especially when one of them doesn't even have an icon.

Experimental options are very much "adjusting the difficulty" of the beatmap, especially with dual notes being proven to be very much playable with cursor too.

Also delete legacy converter, nobody cares about it or compares with newer one.

[LumpBloom7]

It's very much affecting the conversion too.