How to remove the single dot before each chapter in the TOC and make it smaller?

I want to remove the single dot as circled in the picture. Using the thesis class, the single dot appears and and the toc size becomes bigger. Changing to the report class, the dot disappears and the toc size becomes normal. I need to use the thesis class to comply with the requirements set by my university.

Here’s my code:

documentclass[a4paper,12pt]{thesis}
usepackage[Sonny]{fncychap}
usepackage{fullpage}
usepackage{algorithm}
usepackage{titlesec}
titleformat{section}{normalfontfontsize{12}{12}bfseries}{thesection}{0.5em}{}
titleformat{chapter}[display]
{normalfontfontsize{12}{12}bfseriescentering}{chaptertitlename thechapter}{12pt}{}
titleformat{subsection}{normalfontfontsize{12}{12}bfseries}{thesubsection}{0.5em}{}
usepackage{chngcntr}%
renewcommand{thechapter}{}%
renewcommand{thesection}{arabic{chapter}.arabic{section}}%
counterwithout{figure}{chapter}
usepackage[top=2.54cm, bottom=2.54cm, left=4cm, right=2.54cm]{geometry}
usepackage{setspace}
usepackage{fancyhdr}
pagestyle{fancyplain}
fancyhf{}
cfoot{thepage}
renewcommand{headrulewidth}{0pt}


bibliographystyle{plain}
setcounter{secnumdepth}{3}
setcounter{tocdepth}{3}
pagenumbering{roman}
renewcommand{contentsname}{TABLE OF CONTENTS}
usepackage{tocloft}

begin{document}
newcounter{rom}
input{tex/title}newpagethispagestyle{plain}
addtocounter{rom}{1}setcounter{page}{2}~
newpagethispagestyle{plain}setcounter{page}{3}

tableofcontents

newpagethispagestyle{plain}~
clearpage
pagenumbering{arabic}

input{tex/introduction}newpagecleardoublepage
end{document}