Issues in the splitscreen kart selection screen

[Alayan-stk-2]

• When a new player uses the fire key, the screen is supposed to assign a different player name to the new player. This doesn't work anymore, it has to be changed manually to not get a conflict.
• I got a crash when clicking/typing the username selector, but I'm not sure what steps led to it. First player had already a kart selected and I was trying to select the second one.
• The button to edit favorites should not be present, it's only going to be a cause of trouble when two or more players want to select a kart to play with
• Keyboard selection can get stuck in the kart search bar, requiring a mouse click to get unstuck
• The kart search bar and the kart class selectors can also be troublesome with two players wanting to do different things, although I am not sure if they should be removed entirely.