Petab import in try/except clause that fails when amici is not available about pypesto HOT 3 CLOSED

I would not see a specific reason to keep it in the try except clause. pypesto.petab has to be imported separately and at this stage I think we can expect people to have installed petab. What do you think @dweindl, @Doresic?

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Yeah, think it can be moved outside.
A thought: I remember I had to do this for my ordinal/semiquantitative stuff even though they should only ever be used with those two included. If I didn't do it, some tests that do not install petab/amici would fail. However, I was always surprised by how and why these tests would import those modules then. Back then I didn't understand it much / think twice. But there might be something weird there.

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closed in #1355

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