how to draw a bicolor tcolorbox without frame?

You can use frame hidden

 \documentclass{article}
\usepackage{lmodern}
\usepackage[most]{tcolorbox}

\begin{document}

\begin{tcblisting}{bicolor, colback=blue!15,
         colbacklower=white, boxrule=0pt,frame hidden}
This is an example of a \emph{bicolor} \texttt{tcolorbox}
\end{tcblisting}

\end{document}

Not sure if this is what you wanted, but you can add \tcbset{colframe=white} to your preamble (or locally).

Output

Code

\documentclass{article}
\usepackage{lmodern}
\usepackage[most,listings]{tcolorbox}

\tcbset{colframe=white}

\begin{document}

\begin{tcblisting}{bicolor, colback=blue!15,colbacklower=white, boxrule=0pt}
This is an example of a \emph{bicolor} \texttt{tcolorbox}
\end{tcblisting}

\end{document}