the application autocomplete the rest/silences.. it means that you can't have an empty measure. if you remove a quarter beat, a new will created.
if you really want to have 1 less beat.. you have to change the timesignature of your measure.
i mean, if you have a 4/4 time signature, you will have 4 quarter beats.. now if you set it to 3/4, you are going to have 3 quarter beats.