Removed some unused imports

problem33.py

 #!/usr/bin/env python
 from __future__ import division
-from itertools import combinations, permutations
+from itertools import combinations
 from utils import gcd
 
 nrs = [(i, str(i)) for i in xrange(10, 100)]

problem49.py

 #!/usr/bin/env python
 from itertools import permutations, combinations
-from utils import primes_until, digits, add
+from utils import primes_until, add
 from sys import exit
 
 def concat(digits):

problem50.py

 #!/usr/bin/env python
-from math import sqrt
 from utils import primes_until
 
 def maxprime(n):

problem79.py

 #!/usr/bin/env python
-from itertools import permutations
-
 codes = [319, 680, 180, 690, 129, 620, 762, 689, 762, 318, 368, 710, 720, 710,
          629, 168, 160, 689, 716, 731, 736, 729, 316, 729, 729, 710, 769, 290,
          719, 680, 318, 389, 162, 289, 162, 718, 729, 319, 790, 680, 890, 362,