Use a css editor, and place the following rule in order to overwrite itself.
div[id^=google-maps-builder] .gm-style-iw, div[id^=google-maps-builder] .gm-style-iw>div {
overflow: hidden !important;
}
a better way is to install the “Hide Page & Post Titles” plugin which allows you to choose show or hide in the edit mode of pages or posts.
