Remove the use of <main> on Graph Explorer as there is already another main landmark.

[thewahome]

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Desktop (please complete the following information):

OS: [e.g. iOS]
Browser [e.g. chrome, safari]
Version [e.g. 22]

Smartphone (please complete the following information):

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OS: [e.g. iOS8.1]
Browser [e.g. stock browser, safari]
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Additional context
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AB#5813