remove UI for "email notification type" - fixes #855

What does this MR do?

no live code looks at these settings, let's not confuse users pretending they can set

also, no live code sends any of these notifications via email!

maybe, after #718, we can revisit this

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requested review from @CenTdemeern1, @julia, @luna, @Marie, and @tess

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mentioned in commit 6c8d1462

merged