Removing horizontal space in enumerate

Question

How can I remove the space between 1.1. and (1)?

Edit: @barbarabeeton's answer removes the space as required but I had a follow up question of whether there is a way to indent "Remark" with the body of the paragraph (1). Basically to have "Nullam" right below "Remark"in the following image:

MWE:

\documentclass[11pt]{amsart}
\usepackage[left=2cm,top=1cm,right=2cm,nohead,nofoot]{geometry}
\usepackage{amsmath, amssymb}
\usepackage{amsthm}
\usepackage[shortlabels]{enumitem}
\theoremstyle{plain}
\newtheorem{Theorem}{Theorem}[section]
\theoremstyle{definition}
\newtheorem{remark}[Theorem]{Remark}

\begin{document}
\section{A}
\begin{remark}
\begin{enumerate}[leftmargin=*]
    \item ABC
    \item ABC
\end{enumerate}
\end{remark}
\end{document}

Answer 1

You may be interested in something a little more simplistic. Setting your own list-like environment:

\documentclass{amsart}

\usepackage{amsthm}
\usepackage{lipsum}

\theoremstyle{plain}
\newtheorem{Theorem}{Theorem}[section]
\theoremstyle{definition}
\newtheorem{remark}[Theorem]{Remark}

\newcounter{remarkitem}
\newenvironment{remarklist}{%
  \setcounter{remarkitem}{0}% Restart counter
  \setlength{\parindent}{0pt}%
  \renewcommand{\item}{\par
    \refstepcounter{remarkitem}%
    \ifnum\value{remarkitem}=1
      \hspace*{-0.5ex}%
    \fi
    \mbox{(\theremarkitem)}%
    \nobreakspace
  }
}{%
  \par\addvspace{.5\baselineskip}%
}

\begin{document}

\section{A section}
See number~\ref{list:first} and~\ref{list:second}.
\begin{remark}
  \begin{remarklist}
    \item\label{list:first} \lipsum*[1]
    \item\label{list:second} \lipsum*[2]
  \end{remarklist}
\end{remark}

\end{document}