How to remove brace reminder after adding an horizontal frame

Hi,

I have this exercice to do (it's not a score, but more of an exercises sheet) and I want four measures that are separated from one another, so I added an horizontal frame between each. Unfortunately, the brace repeats itself for each separate measures. When I try to remove it, it removes all braces from my score.

Would someone have an idea how to fix that? Thanks!