bcat: Disable Boxcat backend by default

This commit disables the Boxcat backend by default for new users of yuzu.

There's several reasons as to why this is done:
1. Boxcat currently only actually has an impact on 3 games and doesn't influence any core mechanics of them
2. It causes a plethora of issues when enabled such as games like Crash Team Racing, Diablo 3 and Tales of Vesperia not booting at all or hanging
3. It causes https://github.com/yuzu-emu/yuzu/issues/2957 to happen. This makes the configuration menu totally unusable for many Linux users of yuzu

I think those points show that currently the negative impact of Boxcat outweighs its benefits and should therefore be disabled by default.
For users who are eager to use the extra features provided by it, they can still just turn it on in the settings.