return a sorted list of all of the structural variant callers run

def _get_sv_callers(items):
    """
    return a sorted list of all of the structural variant callers run
    """
    callers = []
    for data in items:
        for sv in data.get("sv", []):
            callers.append(sv["variantcaller"])
    return list(set([x for x in callers if x != "sv-ensemble"])).sort()