Describe the bug
There are still styles targetting the wp-block-subhead class in the Gutenberg editor block-library styles.

To reproduce
Steps to reproduce the behavior:

1. Insert cover block.
2. Add some text to it.
3. Inspect the text element.
4. In developer tools, open the Computed tab.
5. Expand color attribute.
6. Notice that the inherit value stems from the Gutenberg editor block-library styles.css.

Expected behavior
As the Subhead block had been retired from Gutenberg for many months,
there shouldn't be any Subhead block related styles left, not even for backward compatibility,
because there had also been a deprecation phase.