Found something: inc/inline-css.min.php seems to create the style tag.
There is a
add_action( ‘wp_head’, ‘puresimple_theme_customize_css’);
I tried using
remove_action( ‘wp_head’, ‘puresimple_theme_customize_css’)
in my functions.php but that doesn’t seem to work. The style tag is still beeing created.
I could comment the add_action call, but I don’t want to make changes in the original. Any idea?