Remove sx prop support from the Timeline component

[liuliu-dev]

Closes #5815

• Removed sx and BoxWithFallback from Timeline component
• Deleted the sxProp test and the dev story with sx.
• Updated Timeline and child components in styled-react.

Need to do changes in github-ui since it's still using Timeline component with sx

Rollout strategy

• Major release; if selected, include a written rollout or migration plan

[changeset-bot]

🦋 Changeset detected

Latest commit: 9396b07

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

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Major
@primer/styled-react	Major

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	89.79 KB (+0.04% 🔺)
packages/react/dist/browser.umd.js	89.86 KB (-0.03% 🔽)

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/3050

[primer-integration]

🟢 ci completed with status success.