Removing an incorrect reference to the content of the next lesson.

[Bongo50]

Website change review checklist:

• [ ] I have requested a review from the appropriate persons
• [ ] I have checked that my changes work in the preview
• [ ] I have checked that the rest of the site is still functioning in the preview
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This pull request:

-Removes areference to the next lesson being about connected rates of change as this is not the next lesson, the next lesson actually being about e.

[kurtbruns]

Thank you!