[FEATURE] Remove auto theme switch based on OS appearance

[muuvmuuv]

Is your feature request related to a problem? Please describe.

Because I'm going to implement this feature natively to VS Code, this isn't longer needed in Sundial.

Describe the solution you'd like

Remove it from Sundial core and add a hint that any other feature in Sundial would need the options in Code colorThemeAutoSwitch to be off (or whatever the option will be named in release)

Describe alternatives you've considered

None

Additional context

• Depends on: [themes] setting for preferred light and dark color theme based on system dark mode setting (Windows/Mac) microsoft/vscode#61519

[mikestopcontinues]

Thanks for all the work you're doing on this. It's totally ace!