el.innerText = el.innerText.split(' ').slice(0, -1).join(' ');
// или
el.innerText = el.innerText.replace(/\s\S+$/, '');
// или
el.innerText = el.innerText.match(/.+(?=\s)/);
// или
el.innerText = el.innerText.slice(0, el.innerText.lastIndexOf(' '));