[Tests]Clear object attributes for open and wpa networks

Destroy open and wpa network list before starting the next testclass.

Bug: 65127132
Test: Manual

Change-Id: I44e9917308693f72da3831320b83db7cb7032465
diff --git a/acts/tests/google/wifi/WifiNetworkSelectorTest.py b/acts/tests/google/wifi/WifiNetworkSelectorTest.py
index a648c46..b52946d 100644
--- a/acts/tests/google/wifi/WifiNetworkSelectorTest.py
+++ b/acts/tests/google/wifi/WifiNetworkSelectorTest.py
@@ -77,6 +77,11 @@
         self.dut.take_bug_report(test_name, begin_time)
         self.dut.cat_adb_log(test_name, begin_time)
 
+    def teardown_class(self):
+        if "AccessPoint" in self.user_params:
+            del self.user_params["reference_networks"]
+            del self.user_params["open_network"]
+
     """ Helper Functions """
 
     def add_networks(self, ad, networks):