Remove duplicate H1/subtitle from trace API docs

[AlvaroLuken]

Motivation

• Several trace reference pages contained a duplicated H1 and subtitle below their frontmatter causing duplicate headings in the rendered site.
• The frontmatter title and description should be used by Fern, so the inline H1/subtitle are unnecessary and cause duplication.

Description

• Removed the leading inline H1 and subtitle blocks that duplicated frontmatter content from four files: what-is-trace-transaction.mdx, what-is-trace-filter.mdx, what-is-trace-block.mdx, and trace-call-vs-debug-tracecall.mdx.
• Kept the existing frontmatter (title, description, subtitle, slug) intact and adjusted the first content heading to the proper section (# Prerequisites or # Introduction).

Testing

• Repo pre-commit tasks ran via lint-staged, executing eslint --fix and prettier --write, and both completed successfully during commit.
• No functional or unit tests were required for these content-only changes.

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Codex Task

[github-actions]

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