The Solution

The short answer is that you can’t easily remove the parallax, but you can set your Site Layout to Boxed, which is not parallax-enabled.  Of course, this will box your layout, so if you want the layout to be full-width, you may add the following to the Custom CSS or your child theme stylesheet:

#wrapper.boxed,
#wrapper.boxed #header-container,
#wrapper.boxed .slider
{
    max-width: 100%;
}
If you also want to stop the header from sticking on scroll:
#wrapper.boxed #header-container{
    position: fixed;
}
#content-container{
     padding: 0;
}