Remove six[7]

Since our code will only support py3. So remove six is necessary.

Change-Id: I3738118b1898421ee41e9e2902c255ead73f3915

watcher/decision_engine/solution/base.py

@@ -56,13 +56,11 @@ Two approaches to dealing with this can be envisaged:
 """
 
 import abc
-import six
 
 from watcher.decision_engine.solution import efficacy
 
 
-@six.add_metaclass(abc.ABCMeta)
-class BaseSolution(object):
+class BaseSolution(object, metaclass=abc.ABCMeta):
     def __init__(self, goal, strategy):
         """Base Solution constructor
 

watcher/decision_engine/solution/solution_comparator.py

@@ -17,11 +17,9 @@
 # limitations under the License.
 #
 import abc
-import six
 
 
-@six.add_metaclass(abc.ABCMeta)
-class BaseSolutionComparator(object):
+class BaseSolutionComparator(object, metaclass=abc.ABCMeta):
     @abc.abstractmethod
     def compare(self, sol1, sol2):
         raise NotImplementedError()

watcher/decision_engine/solution/solution_evaluator.py

@@ -17,11 +17,9 @@
 # limitations under the License.
 #
 import abc
-import six
 
 
-@six.add_metaclass(abc.ABCMeta)
-class BaseSolutionEvaluator(object):
+class BaseSolutionEvaluator(object, metaclass=abc.ABCMeta):
     @abc.abstractmethod
     def evaluate(self, solution):
         raise NotImplementedError()