Remove GTK theming

[GamzeeRakoon]

Hello,

Forcing GTK theming can lead to inconsistent application displays and broken functionality. This often results in misaligned or out-of-place UI elements, significantly degrading the overall user experience. Furthermore, some applications may fail to render correctly or encounter functional issues due to the enforced theme, which cannot be disabled. This behavior is particularly frustrating for users who prefer applications in their default, unthemed state.

For reference, you can learn more about this issue here: https://stopthemingmy.app/

Notably, plain Fedora has already discontinued shipping its own GTK theming. I believe adopting a similar approach in Bazzite would greatly benefit users by providing a more consistent and reliable experience