Don't get rid of z item when using z move (#801)

* don't get rid of z item when using z move

* fix test

Author: cameronangliss

src/poke_env/battle/abstract_battle.py

@@ -899,7 +899,6 @@ def parse_message(self, split_message: List[str]):
             else:
                 self._opponent_used_z_move = True
             pokemon = event[2]
-            self.get_pokemon(pokemon).used_z_move()
         elif event[1] == "clearpoke":
             self.in_team_preview = True
             for mon in self.team.values():

src/poke_env/battle/pokemon.py

@@ -675,9 +675,6 @@ def _update_from_teambuilder(self, tb: TeambuilderPokemon):
             for stat, val in zip(["hp", "atk", "def", "spa", "spd", "spe"], stats):
                 self._stats[stat] = val
 
-    def used_z_move(self):
-        self._item = None
-
     def was_illusioned(self, fields: Dict[Field, int]):
         self._current_hp = None
         self._max_hp = None

unit_tests/environment/test_battle.py

@@ -413,7 +413,6 @@ def test_battle_request_and_interactions(example_request):
 
     battle.opponent_active_pokemon.item = "grassiumz"
     battle.parse_message(["", "-zpower", "p1: Sunflora"])
-    assert battle.opponent_active_pokemon.item is None
 
     sunflora = battle.opponent_active_pokemon
     assert sunflora.fainted is False