How to remove automatically added custom style tag?

In my case the style tag was added by the flying font plugin. I have modified the file ‘wp-content/plugins/flying-fonts/flying-fonts.php’

................
$style =
"<style>body{font-family:-apple-system,system-ui,BlinkMacSystemFont,'Segoe UI',Roboto,Oxygen,Ubuntu,Cantarell,'Fira Sans','Droid Sans','Helvetica Neue',sans-serif !important}code{font-family:Menlo,Consolas,Monaco,Liberation Mono,Lucida Console,monospace !important}</style>";
$style=""; // set the style as ''
$html = str_replace('</head>', $style . '</head>', $html);
.........

And i have added the style manually in non AMP page header.