Update rct1 go karts & toilets thumbnails.

[ZeeMaji]

Some updates for two of the rct1 ride object thumbnails to improve their accuracy and fix errors.

For the go karts the beta rock edge is used now that i have restored it as that was the edge used in the original thumbnail. I also fixed an incorrect terrain shape in the bottom right although it's still not perfect due to some oddities with the grass sprites in the original thumbnail. And i also fixed some errors i made when masking the purple and blue karts from the original thumbnail as some pixels of their sprites were missing.

Original go karts thumbnail as a refresher

For the toilets i have recreated the entire scene of the original thumbnail from scratch, accuracy wise it's now nearly perfectly accurate to the original rct1 thumbnail even down to the placement and colors of the guests.

Original RCT1 toilets thumbnail as a refresher, since we've used the current openrct2 icon for a few years now.