Add this code to the Custom CSS field on the More tab of your Facebook Feed widget’s settings:
.eapps-facebook-feed-videos-item:nth-child(n+5),
.eapps-facebook-feed-videos-load-more {
display: none !important;
}
If you wish to display a different number of videos, just subtract 1 from the desired amount and input it in the brackets at the end of the 1st line.