Add 64px headline typography presets

[jamesmockett]

What are you changing?

• Adds 64px variant of headline typography presets and removes 70px variant

headlineBold64
headlineLight64
headlineLightItalic64
headlineMedium64
headlineMediumItalic64

Why?

• Maintains parity with presets in Figma and supports new use cases
• The 70px variant had been erroneously added

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 4d67fe94ec484821bbe4efde2c3ab17d14dd83da

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

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[github-actions[bot]]

[!TIP] Once this PR is ready to go, add the run_chromatic label to run the Chromatic tests.

This saves us a lot of money by not running the tests before we need them.