Issue #2334. Ensure that we consider browser-sent images as valid.

[miketaylr]

r? @zoepage

npm run test:js -- --grep="remove image upload button"

[miketaylr]

The bug is that without the .is-validated class, it never gets a higher z-index which is controlled by this selector, so you can't actually click it:

.is-validated .label-remove {
    visibility: visible;
    z-index: 40;
    cursor: pointer;
    border: 0 none;
    outline: 0;
}

[zoepage]

LGTM! :)))