There's no theme option to do this, because in some cases the breadcrumb provides useful navigation beyond what is available in the normal navbar.

e.g., if you're inside an app like Photo Album of Forums, then the breadcrumb will show which album/forum you are in.

If you really really want to remove it, you can do so with a bit of custom CSS. The only bit of extra CSS you need is:

.breadcrumb {
  display: none;
}

You can add this by creating a file on your computer "custom.css" or whatever, adding this rule, then uploading it into your Assets Library of your site. In the Bootstrap theme options you can then select this file from the Assets Library in the Extra CSS File option.

Thanks

Joe - Voice Admin