Remove obsolete abstractoff option

[juliangeissler]

Fixes warning:

Class scrreprt Warning: You've used obsolete option abstractoff'. (scrreprt) Usage of this option indicates an old document (scrreprt) and changes compatibility level using (scrreprt) abstract=false,version=first,
(scrreprt) enabledeprecatedfontcommands' that may result
(scrreprt) in further warnings.
(scrreprt) If you don't want this, you should simply
(scrreprt) replace option abstractoff' by abstract=false'.

Basically you can replace 'abstractoff' by 'abstract=false'

But after reading the packages documentation, you can remove it already because false is the default

See german doc, page 74, 3.8 Zusammenfassung, Paragraph abstract=Ein-Aus-Wert
http://mirrors.ctan.org/macros/latex/contrib/koma-script/doc/scrguide.pdf

Package-Link; https://ctan.org/pkg/scrreprt