Maybe listof=flat
does what you want:
\documentclass[
listof=flat
]{scrbook}
\begin{document}
\listoftables
\cleardoubleemptypage
\begin{table}[tbp]
\centering
\captionabove{Test}
\label{tab:t}
\begin{tabular}{cccc}
\end{tabular}
\end{table}
\end{document}

With listof=flat
the needed numwidth
for the numbers is measured. So it needs an additional run.
Update:
I would still suggest to use option listof=flat
. But since version 3.20 you can also set the indent
for table
and figure
in the lists directly using:
\DeclareTOCStyleEntry[indent=0pt]{tocline}{table}
\DeclareTOCStyleEntry[indent=0pt]{tocline}{figure}
Then the default numwidth
(2.3em) will not be changed.

Code:
\documentclass[
captions=tableheading
]{scrbook}[2016/05/10]
\DeclareTOCStyleEntry[indent=0pt]{tocline}{table}
\DeclareTOCStyleEntry[indent=0pt]{tocline}{figure}
\begin{document}
\listoftables
\cleardoubleemptypage
\begin{table}[tbp]
\centering
\caption{Test}
\label{tab:t}
\begin{tabular}{cccc}
\end{tabular}
\end{table}
\end{document}
Remark: Use \captionabove
instead \caption
if the caption is a heading. Then you get the correct space between the caption and the table. If all table captions are headings it is also possible to use the class option captions=tableheading
and \caption
. See the documentation for more information.