Remove unused imports

15_goblins.py

@@ -1,7 +1,6 @@
 #!/usr/bin/env python3
 import sys
 from operator import attrgetter
-from collections import defaultdict
 
 SPACE, WALL = 0, 1
 GOBLINS, ELVES = 0, 1

16_opcodes.py

@@ -1,6 +1,5 @@
 #!/usr/bin/env python3
 import sys
-from collections import defaultdict
 
 isa = {
     'addr': lambda a, b, reg: reg[a] + reg[b],

18_lumber.py

@@ -1,6 +1,5 @@
 #!/usr/bin/env python3
 import sys
-import time
 
 OPEN, TREE, LUMB = range(3)