Remove unused password in test_live_block_migration

In LiveBlockMigrationTestJSON, self.password exists but it is not
used at all. So this patch removes it.

Change-Id: Ie699955728850aebb9f575c50bad12673bd9fe42
diff --git a/tempest/api/compute/test_live_block_migration.py b/tempest/api/compute/test_live_block_migration.py
index 92a1c86..6da6b79 100644
--- a/tempest/api/compute/test_live_block_migration.py
+++ b/tempest/api/compute/test_live_block_migration.py
@@ -71,8 +71,6 @@
         else:
             server = self.create_test_server(wait_until="ACTIVE")
             server_id = server['id']
-            self.password = server['adminPass']
-            self.password = 'password'
             self.created_server_ids.append(server_id)
             return server_id