Extract arrays.delete() to core/utils

I've cloned the array using `slice()` without argument (which is what underscore's` _.clone()` does for arrays: http://underscorejs.org/docs/underscore.html#section-88)
What about:

    var index = array.indexOf(value);
    if(index == -1) return array;
    array = clone(array);
    array.splice(index, 1);
    return array;

WDYT?