(#423) Updates nci logo in header

[dlescarbeau]

• removes aria label from anchor

• adds alt text value to image

Closes #423

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[github-actions[bot]]

Viewing Information

• The documentation site
• NCIDS JS Documentation
• The storybook site
• The example site

[andyvanavery31]

@dlescarbeau could you please update the alt-text in the actual Doc Site header (not the component page) to be "National Cancer Institute Design System Homepage"?