[API-702] v5 SQL: Remove unused load balancer methods (#458)

* v5 SQL: Remove unused load balancer methods

These methods were specially added for 4.2 SQL, but they are unused
in v5. Hence, we are removing the unused methods and reverting the
changes we made around the load balancer implementations and tests.

Note that, it is perfectly safe to remove these methods in Python.
If there were users that implemented these methods, they can use
their code without changing anything.

* add explicit mappings

hazelcast/util.py

@@ -276,61 +276,18 @@ def next(self):
         """
         raise NotImplementedError("next")
 
-    def next_data_member(self):
-        """Returns the next data member to route to.
-
-        Returns:
-            hazelcast.core.MemberInfo: The next data member or
-            ``None`` if no data member is available.
-        """
-        return None
-
-    def can_get_next_data_member(self):
-        """Returns whether this instance supports getting data members
-         through a call to :func:`next_data_member`.
-
-        Returns:
-            bool: ``True`` if this instance supports getting data members.
-        """
-        return False
-
-
-class _Members(object):
-    __slots__ = ("members", "data_members")
-
-    def __init__(self, members, data_members):
-        self.members = members
-        self.data_members = data_members
-
 
 class _AbstractLoadBalancer(LoadBalancer):
     def __init__(self):
         self._cluster_service = None
-        self._members = _Members([], [])
+        self._members = []
 
     def init(self, cluster_service):
         self._cluster_service = cluster_service
         cluster_service.add_listener(self._listener, self._listener, True)
 
-    def next(self):
-        members = self._members.members
-        return self._next(members)
-
-    def next_data_member(self):
-        members = self._members.data_members
-        return self._next(members)
-
-    def can_get_next_data_member(self):
-        return True
-
     def _listener(self, _):
-        members = self._cluster_service.get_members()
-        data_members = [member for member in members if not member.lite_member]
-
-        self._members = _Members(members, data_members)
-
-    def _next(self, members):
-        raise NotImplementedError("_next")
+        self._members = self._cluster_service.get_members()
 
 
 class RoundRobinLB(_AbstractLoadBalancer):
@@ -345,7 +302,8 @@ def __init__(self):
         super(RoundRobinLB, self).__init__()
         self._idx = 0
 
-    def _next(self, members):
+    def next(self):
+        members = self._members
         if not members:
             return None
 
@@ -358,7 +316,8 @@ def _next(self, members):
 class RandomLB(_AbstractLoadBalancer):
     """A load balancer that selects a random member to route to."""
 
-    def _next(self, members):
+    def next(self):
+        members = self._members
         if not members:
             return None
         idx = random.randrange(0, len(members))