[Major] Remove legacy color support

[langermank]

This PR removes support for color themes. Going forward, Primer expects an explicit color theme import directly from primer/primitives.

@import '@primer/primitives/dist/css/functional/themes/light.css';
@import '@primer/primitives/dist/css/functional/themes/light-tritanopia.css';
@import '@primer/primitives/dist/css/functional/themes/light-high-contrast.css';
@import '@primer/primitives/dist/css/functional/themes/light-colorblind.css';
@import '@primer/primitives/dist/css/functional/themes/dark.css';
@import '@primer/primitives/dist/css/functional/themes/dark-colorblind.css';
@import '@primer/primitives/dist/css/functional/themes/dark-dimmed.css';
@import '@primer/primitives/dist/css/functional/themes/dark-high-contrast.css';
@import '@primer/primitives/dist/css/functional/themes/dark-tritanopia.css';

This is a breaking change and marked as such.

[changeset-bot]

🦋 Changeset detected

Latest commit: d777f6c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/css	Major

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