Remove deprecated design tokens from codebase

The following semantic color tokens are non-standard (Figma never declared them) and should be removed from the codebase to improve the consistency between environments.

```
// static/css/v3/themes.css
--color-bg-primary: var(--color-primary-black);
--color-bg-secondary: var(--color-primary-grey-950);
--color-border: var(--color-primary-grey-800);
```

```
// static/css/v3/semantics.css
--color-bg-primary: var(--color-secondary-light-blue);
--color-bg-secondary: var(--color-primary-white);
--color-border: var(--color-primary-grey-300);
```