Better `make_query` output

[mccalluc]

def make_query(code_gen, identifier, accuracy_name, stats_name):
    def template(dp, GROUP_NAMES, stats_context, EXPR_NAME):
        groups = GROUP_NAMES
        QUERY_NAME = (
            stats_context.query().group_by(groups).agg(dp.len(), EXPR_NAME).WITH_KEYS
            if groups
            else stats_context.query().select(EXPR_NAME)
        )
        STATS_NAME = QUERY_NAME.release().collect()
        STATS_NAME  # type: ignore

    return (
        DefaultsTemplate(template)
        .fill_values(
            GROUP_NAMES=list(code_gen.analysis_plan.groups.keys()),
        )

We know whether GROUP_NAMES is going to be empty or not, so we can get rid of the conditional logic inside the template. I generally want to to move conditional logic outside the template, unless it serves a pedagogical purpose, and doesn't make things much more cluttered. I think this fails on both counts.