Your picture needs to be from farther back. We can't see the hearth or a mantle. The arch detail is sitting proud of the field of the chimney? I do not think just knocking it off is an option. If you do be prepared to clad the entire chimney in a slab stone or dry wall...The hearth protects kids/you from touching the HOT glass once your insert if fully installed. Not sure what your complaint is about it as it is not shown. Perhaps you want to put the slab stone on the floor and convert to a not raised hearth??? More pictuers and information/idea/inspiration board is needed.

Click on the picture and you can see more. My first impression is no, not easily without damaging the brick underneath. You will still need a hearth of proper depth and width at the level of the floor as well.

It's hard to tell from pictures if the arch bricks were placed on top of the flat bricks or if the flat bricks were cut around the arch. That's what is going to determine if the arch can be removed.

I was able to 'legally' remove the hearth from my gas fireplace when I added an electric insert. The building inspector said even though the electric insert has a heat option, there wasn't a fire hazard to the flammable flooring. Check your local building codes.