renku: automatic removal of outputs

data/politicians/yearly_csvs/1910_MPs.csv

data/politicians/yearly_csvs/1911_MPs.csv

data/politicians/yearly_csvs/1912_MPs.csv

data/politicians/yearly_csvs/1913_MPs.csv

data/politicians/yearly_csvs/1914_MPs.csv

data/politicians/yearly_csvs/1915_MPs.csv

data/politicians/yearly_csvs/1916_MPs.csv

data/politicians/yearly_csvs/1917_MPs.csv

data/politicians/yearly_csvs/1918_MPs.csv

data/politicians/yearly_csvs/1919_MPs.csv

data/politicians/yearly_csvs/1920_MPs.csv

data/politicians/yearly_csvs/1921_MPs.csv

data/politicians/yearly_csvs/1922_MPs.csv

data/politicians/yearly_csvs/1923_MPs.csv

data/politicians/yearly_csvs/1924_MPs.csv

data/politicians/yearly_csvs/1925_MPs.csv

data/politicians/yearly_csvs/1926_MPs.csv

data/politicians/yearly_csvs/1927_MPs.csv

data/politicians/yearly_csvs/1928_MPs.csv

data/politicians/yearly_csvs/1929_MPs.csv