Remove checkbox for database.DBexport

[jacklul]

Small thing - maybe it was missed or is not yet being used in FTL config...?

What does this PR aim to accomplish?:

Remove checkbox for non-existent config key database.DBexport introduced in 74baa97, it seems to never ended up being used as database.maxDBdays=0 disables the database anyway (as description states).
It does not seem to exist in FTL config.

How does this PR accomplish the above?:

Removes the whole div for the checkbox section and updates data-configkeys attribute.

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[rdwebdesign]

maybe it was missed or is not yet being used in FTL config...?

It was missed.
We removed the option from FTL, but it was forgotten here.